Amicus Curiae Brief — Okello T. Chatrie, Petitioner v. United States
Supreme Court briefMar 2, 2026
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No. 25-112
In the Supreme Court of the United States
_________
O KELLO T. CHATRIE ,
v.
Petitioner,
U NITED S TATES OF A MERICA,
Respondent.
_________
On Writ Of Certiorari
To The United States Court Of Appeals
For The Fourth Circuit
_________
BRIEF OF X CORP. AS AMICUS CURIAE
IN SUPPORT OF PETITIONER
_________
AMY P EIKOFF
Pacific Legal Foundation
3100 Clarendon Blvd.,
Suite 1000
Arlington, VA 22201
(202) 888-6881
apeikoff@pacificlegal.org
MARK MILLER
Counsel of Record
Pacific Legal Foundation
4440 PGA Blvd.,
Suite 307
Palm Beach Gardens, FL
33410
(561) 691-5000
mark@pacificlegal.org
Counsel for Amicus Curiae X Corp.
TABLE OF CONTENTS
Identity and Interest of Amicus Curiae ..................... 1
Introduction and Summary of the Argument ............ 2
Argument .................................................................... 4
I. Miller and Smith Dramatically Expanded
the Scope of the Third-Party Doctrine
Without Justification ........................................ 4
II. Attempts to Provide Normative
Justifications for the Doctrine Fail................... 7
III. Recasting the Third-Party Doctrine as
“Consent” or “Disclosure” Only Raises
More Questions................................................ 11
IV. Coda: What about Katz? ................................. 19
Conclusion ................................................................. 24
ii
TABLE OF AUTHORITIES
Page(s)
Cases
Carpenter v. United States,
585 U.S. 296 (2018) .......... 6, 9-10, 12, 15-18, 20-24
Case v. Montana,
146 S. Ct. 500 (2026) ........................................... 18
Hale v. Henkel,
201 U.S. 43 (1906) ................................................. 9
Hanover Nat’l Bank of City of New York
v. First Nat’l Bank of Burlingame,
109 F. 421 (8th Cir. 1901) ............................... 5, 17
Ex parte Jackson,
96 U.S. 727 (1877) ............................... 12-13, 15-16
Katz v. United States,
389 U.S. 347 (1967) ............................. 17-19, 23-24
Kyllo v. United States,
533 U.S. 27 (2001) ................................... 15, 21, 24
Minnesota v. Carter,
525 U.S. 83 (1998) .............................................. 23
Smith v. Maryland,
442 U.S. 735 (1979) ............... 2-7, 16, 20, 22, 24-25
United States v. Chatrie,
136 F.4th 100 (4th Cir. 2025) ..................... 3, 20-23
United States v. Dionisio,
410 U.S. 1 (1973) ................................................... 9
United States v. Jones,
565 U.S. 400 (2012) ........ 1, 14-15, 17-19, 21-22, 24
United States v. Miller,
425 U.S. 435 (1976) ..................... 2-7, 16, 20, 24-25
United States v. Smith,
110 F.4th 817 (5th Cir. 2024) .............................. 21
iii
United States v. White,
401 U.S. 745 (1971) ....................................... 11, 23
Regulation
Exec. Order No.14243,
90 Fed. Reg. 13681 (Mar. 20, 2025) ...................... 4
Rule
Sup. Ct. R. 37.6 ........................................................... 1
Other Authorities
Billings, Autumn, Mass Surveillance Is
Powering a New Era of Pretextual
Traffic Stops, Reason (Nov. 24, 2025,
at 12:37 PM),
https://tinyurl.com/bde8h97h ................................ 4
Brandeis, Louis D. & Warren, Samuel D.,
The Right to Privacy,
4 Harv. L. Rev. 193 (1890) .................................... 5
Cox, Joseph, Inside ICE’s Tool to
Monitor Phones in Entire
Neighborhoods, 404 Media (Jan. 8,
2026, at 9:00 AM),
https://tinyurl.com/bum4h764............................... 4
Epstein, Richard A., Privacy and the
Third Hand: Lessons from the
Common Law of Reasonable
Expectations,
24 Berkeley Tech. L.J. 1199 (2009).............. 7-8, 12
Frenkel, Sheera & Krolik, Aaron,
Trump Taps Palantir to Compile
Data on Americans, The New York
Times (May 30, 2025) ............................................ 4
iv
Fuller, Lon, The Case of the Speluncean
Explorers,
62 Harv. L. Rev. 616 (1949) ........................... 19-20
Holland, H. Brian, A Third-Party
Doctrine for Digital Metadata,
41 Cardozo L. Rev. 1549 (2020) ............................ 2
Issacharoff, Lucas & Wirshba, Kyle,
Restoring Reason to the Third-Party
Doctrine,
100 Minn. L. Rev. 987 (2016) .......................... 2, 10
James, William, The Moral Philosopher
and Moral Life, in The Will to
Believe and Other Essays in Popular
Philosophy (1956) ................................................ 24
Kerr, Orin, The Digital Fourth
Amendment: Privacy and Policing in
Our Online World
(Oxford Univ. Press 2025) .......................... 2, 12-18
Kerr, Orin S., The Case for the ThirdParty Doctrine,
107 Mich. L. Rev. 561 (2009) .............. 2, 7-8, 10-11
Kerr, Orin S., Data Scanning and the
Fourth Amendment,
67 B.C. L. Rev. 431 (2026) .............................. 18-19
Kopel, David, Turning Credit Cards into
Comprehensive Financial
Surveillance, Reason: Volokh
Conspiracy (July 14, 2025 at 2:46
PM), https://tinyurl.com/38zfynan ........................ 4
Murphy, Erin, The Case Against the
Case for Third-Party Doctrine: A
Response to Epstein and Kerr,
24 Berkeley Tech. L.J. 1239 (2009).............. 8-9, 12
v
Peikoff, Amy, L., Beyond Reductionism:
Reconsidering the Right to Privacy,
3 N.Y.U. J.L. & Liberty 1 (2008) ......................... 24
Peikoff, Amy L., Of Third-Party
Bathwater: How to Throw Out the
Third-Party Doctrine While
Preserving Government’s Ability to
Use Secret Agents,
88 St. John’s L. Rev. 349 (2014) ............................ 8
Restatement (Second) of Torts § 217(e)
(1965) ................................................................... 19
Solove, Daniel J., Data Is What Data
Does: Regulating Based on Harm
and Risk Instead of Sensitive Data,
118 Nw. Univ. L. Rev. 1081 (2024) ..................... 16
Story, Joseph, Commentaries on the
Law of Bailments (1832) ..................................... 15
Tuccille, J.D. The ATF Created a
Backdoor Gun Registry. Lawmakers
Want an Explanation, Reason (Feb.
13, 2026 at 7:00 AM),
https://tinyurl.com/3dw852ud ............................... 4
IDENTITY AND INTEREST OF
AMICUS CURIAE 1
“Awareness that the government may be watching
chills associational and expressive freedoms.” United
States v. Jones, 565 U.S. 400, 416 (2012) (Sotomayor,
J., concurring). X Corp., an American technology company headquartered in Bastrop, Texas, strongly
agrees, and strives to protect the associational and expressive freedoms of users of its real-time information-sharing app and associated services. X understands that this means also ensuring its users’ Fourth
Amendment rights are respected regarding the data X
collects and processes.
While providing services to users, X necessarily collects, processes, and stores multiple classes of sensitive user data pertaining to millions of innocent individuals, which could be the subject of “reverse
searches” by law enforcement or other government
agencies, including location information. 2 X believes
contractual promises, like those it makes to its users
in its Terms of Service, should be recognized as relevant to the protection their data receives under the
Fourth Amendment.
1 Pursuant to Rule 37.6, Amicus Curiae affirms that no counsel
for any party authored this brief in whole or in part, and no
counsel or party made a monetary contribution intended to fund
the preparation or submission of this brief. No person other than
Amicus Curiae, their members, or their counsel made a monetary
contribution to its preparation or submission.
2 X may infer the location of its users using multiple signals,
including the user-specified location, the user’s IP address, and—
for the subset of users who consent—device-provided location
data like that at issue in this case. X routinely resists overbroad
or otherwise invalid government demands for user data,
including through litigation.
2
INTRODUCTION AND
SUMMARY OF ARGUMENT
No one realized it then, but this Court’s rulings in
the 1970s third-party doctrine cases, United States v.
Miller, 425 U.S. 435 (1976), and Smith v. Maryland,
442 U.S. 735 (1979), ushered in a privacy-prohibition
era for the twenty-first century. Henceforth, any attempt to selectively share information with one’s service provider would be treated, for Fourth Amendment purposes, as if one had shouted the information
through a megaphone, perched upon the highest
mountaintop, on worldwide livestream.
To this day, Miller and Smith remain essentially
untouched, in part because legal scholars have argued
in justification of the idea that an individual who
shares information with a third party, even for a limited purpose, no longer has a “reasonable expectation
of privacy” in that information. See, e.g., Orin S. Kerr,
The Case for the Third-Party Doctrine, 107 Mich. L.
Rev. 561 (2009) (“Kerr 2009”); H. Brian Holland, A
Third-Party Doctrine for Digital Metadata, 41
Cardozo L. Rev. 1549 (2020); Orin Kerr, The Digital
Fourth Amendment: Privacy and Policing in Our
Online World 133-62 (Oxford Univ. Press 2025) (“Kerr
2025”); see also Lucas Issacharoff & Kyle Wirshba, Restoring Reason to the Third-Party Doctrine, 100 Minn.
L. Rev. 987 (2016) (arguing for retaining the thirdparty doctrine as an exception to the Fourth Amendment’s warrant requirement). And lower courts have
at times leaned on those justifications for support. For
example, Judge Wilkinson, concurring with the en
banc Fourth Circuit, relied upon some of these normative arguments in concluding, “this case involved a
straightforward application of [Miller and Smith].”
3
United States v. Chatrie, 136 F.4th 100, 109 (4th Cir.
2025) (Wilkinson, J., concurring) (citations omitted).
The normative arguments given in support of the doctrine are not persuasive, however. There is a better
way.
X Corp.’s suggestion is straightforward. Using the
common law of contract as a lens to analyze the “secret
agent” cases in which the third-party doctrine arose,
one can see that this Court overextended in Miller and
Smith a doctrine originating in the context of illegal
contract to the context of ordinary business contracts
between law-abiding citizens and their service providers. See Br. of X Corp. as Amicus Curiae in Supp. of
Pet’r at 8-11. Terms of service that promise to protect
the privacy of information shared by users with their
service providers should be treated as the functional
equivalent of “no trespassing” signs on a possession
perhaps more valuable than real property—our personal information (“papers” or “effects”). When privacy-protective terms of service are in place, terms
that recognize users’ rights in the information shared,
collected, or stored, government should typically get a
warrant based on probable cause before gaining access to that information, including by means of “reverse searches” such as the geofence warrant at issue
here.
The adoption of this rule would require, at the very
least, that this Court continue to narrow or distinguish Miller and Smith. This is the right thing to do.
With politicians and government agencies continuously devising new ways to collect, store, aggregate,
4
and search individuals’ selectively shared private information, 3 the time for this Court to affirm Fourth
Amendment protections is at hand.
ARGUMENT
I.
Miller and Smith Dramatically Expanded
the Scope of the Third-Party Doctrine
Without Justification
The common law of contract is the key to understanding the third-party doctrine. This is so for two
reasons. First, given that the Fourth Amendment
arose from concerns about government violating individuals’ common-law rights, analysis of Fourth
Amendment cases in terms of the common-law rights
and interests at stake is the best way to understand
the implications of the Amendment’s original meaning. Br. of X Corp. as Amicus Curiae in Supp. of Pet’r
at 6 (citations omitted). Second, before there was ever
a proposal to recognize a distinct “right to privacy,”
the common law provided legal protection for privacy
via “laws protecting rights to property and contract, or
defending against breaches of trust or confidence[.]”
3 See, e.g., Joseph Cox, Inside ICE’s Tool to Monitor Phones in
Entire Neighborhoods, 404 Media (Jan. 8, 2026, at 9:00 AM),
https://tinyurl.com/bum4h764; Autumn Billings, Mass Surveillance Is Powering a New Era of Pretextual Traffic Stops, Reason
(Nov. 24, 2025, at 12:37 PM), https://tinyurl.com/bde8h97h; Exec.
Order No.14243, 90 Fed. Reg. 13681 (Mar. 20, 2025); Sheera
Frenkel & Aaron Krolik, Trump Taps Palantir to Compile Data
on Americans, The New York Times (May 30, 2025), https://tinyurl.com/5ydt98za; David Kopel, Turning Credit Cards into
Comprehensive Financial Surveillance, Reason: Volokh Conspiracy (July 14, 2025, at 2:46 PM), https://tinyurl.com/38zfynan;
J.D. Tuccille, The ATF Created a Backdoor Gun Registry. Lawmakers Want an Explanation, Reason (Feb. 13, 2026, at 7:00
AM), https://tinyurl.com/3dw852ud.
5
Id. at 12 (citing Louis D. Brandeis & Samuel D. Warren, The Right to Privacy, 4 Harv. L. Rev. 193, 213
(1890)).
In its petition-stage brief, amicus X Corp. argued
that this Court, in Miller and Smith, erroneously expanded the third-party doctrine without justification
by unmooring the Fourth Amendment from the common law of contract. Miller and Smith should at least
be narrowed or distinguished, and the third-party doctrine should be returned to its original and proper
scope set forth in the “secret agent” cases. Specifically, if a party shares information with a third party
subject to an illegal agreement to keep the information confidential, then the contract should be no
bar to a government search of that information. But if
a party shares information with a third party subject
to a legal confidentiality agreement, that arrangement should preserve Fourth Amendment protections. In other words:
If Tony Soprano makes an “arrangement” with a “business associate,” any
collateral promises are unenforceable,
including promises to keep it a secret.
But terms of service agreements between
users and Google or X Corp. would not be
deemed illegal contracts, merely because
some users happened to have also committed crimes or are otherwise properly
subject to government investigation.
Br. of X Corp. as Amicus Curiae in Supp. of Pet’r at 11
(citing Hanover Nat’l Bank of City of New York v. First
Nat’l Bank of Burlingame, 109 F. 421, 425 (8th Cir.
1901) (“The mere fact that a contract the consideration and performance of which are lawful incidentally
6
assists one in evading a law is no bar to its enforcement.”)).
That the common law of contract supplies the key
to understanding the third-party doctrine should
come as no surprise. Legally enforceable 4 promises
made to users by third-party service providers to, e.g.,
safeguard user data and disclose it in only limited,
enumerated circumstances as part of their terms of
service, should be recognized as giving rise to privacy
and property interests entitled to Fourth Amendment
protection. Ibid. (citing Carpenter v. United States,
585 U.S. 296, 399 (2018) (Gorsuch, J., dissenting) (discussing analogy of common-law bailment); Pet’r’s
Opening Br. at 15-16 (demonstrating how, per
Google’s terms of service, “Location History has the
key attributes of ‘property’ as traditionally understood: the right to use, enjoy, dispose, and exclude.”);
Id. at 16-17 (collecting cases in which courts have imposed civil liability for commission of “traditional
property torts” involving unauthorized access to data
held by third-party service providers).
As X Corp. noted in its petition-stage brief, the “justification” offered for the doctrine in Miller was an assumption Congress made in enacting the Bank Secrecy Act, which had “a high degree of usefulness” to
law enforcement. Br. of X Corp. as Amicus Curiae in
Supp. of Pet’r at 9 n.6 (citation omitted). Smith applied the ruling in Miller without further explanation,
even hinting at Miller’s question-begging “justification” in a footnote which read, in part, “[I]f the Government were suddenly to announce on nationwide
4 An example of terms of service that would not be enforceable
would be those of a website that predominantly or exclusively
sells illegal drugs.
7
television that all homes henceforth would be subject
to warrantless entry, individuals thereafter might not
in fact entertain any actual expectation of privacy regarding their homes, papers, and effects.” Smith, 442
U.S. at 740 n.5. See also Richard A. Epstein, Privacy
and the Third Hand: Lessons from the Common Law
of Reasonable Expectations, 24 Berkeley Tech. L.J.
1199, 1207 (2009) (“[T]he reasonable expectations
that flow from knowledge of the law cannot explain
how that law should be configured in the first place.”).
The mere existence of a statute that law enforcement
has found “useful” does not extinguish a “legitimate
expectation of privacy.” In our constitutional republic,
more is required. Miller’s ruling was not properly justified, and Smith was wrong to rely upon it. Instead,
as the Smith footnote concluded, “a normative inquiry
is proper.” Smith, 442 U.S. at 740 n.5. As we’ll see,
the normative justifications for retaining the doctrine
in its current form are not convincing.
II. Attempts to Provide Normative
Justifications for the Doctrine Fail
In the proceedings below, Judge Wilkinson relied
in his concurrence on normative justifications for the
third-party doctrine offered by Professor Orin Kerr.
Professor Kerr’s arguments have been among the
most influential in defending the doctrine, and worth
special consideration. In 2009, he presented two
grounds of support. First, “[w]ithout the doctrine,
criminals could use third-party agents to fully enshroud their criminal enterprises in Fourth Amendment protection.” Kerr 2009, supra, at 576. The doctrine, he argued, would maintain “technological neu-
8
trality,” preserving “roughly the same degree of privacy protection” whether a criminal commits a crime
alone, or with third-party assistance. Id. at 577.
Kerr’s argument fails, however, to account for the
latitude the “secret agent” cases provide to law enforcement. Because an agreement between a criminal
and his third-party agent to enshroud a crime in secrecy would be an illegal contract not subject to Fourth
Amendment protection, see Amy L. Peikoff, Of ThirdParty Bathwater: How to Throw Out the Third-Party
Doctrine While Preserving Government’s Ability to Use
Secret Agents, 88 St. John’s L. Rev. 349, 374-76 (2014),
there is no need to expand the third-party doctrine to
all contracts with third parties to adequately address
Kerr’s concern.
Moreover, Kerr’s argument itself raises substantial
questions. First, “the technologies left exposed by
third-party doctrine are not exclusively deployed for
illicit purposes,” and so the doctrine “dissuad[es] innocent, desirable conduct[.]” Erin Murphy, The Case
Against the Case for Third-Party Doctrine: A Response
to Epstein and Kerr, 24 Berkeley Tech. L.J. 1239, 1241
(2009); see also Epstein, supra, at 1226 (explaining the
doctrine “creates social inefficiencies with respect to
lawful conduct that people naturally wish to keep
from the prying eye of the state.”).
Second, the mere possibility that lawful confidential arrangements may render crime more difficult to
detect without a warrant is not a reason to obliterate
the confidentiality of such arrangements. After all,
the Constitution “[does] not obliterate privacy protections for the home, for instance,” just because the vast
majority of many crimes occur there. Murphy, supra,
at 1244.
9
Moreover, the use of a third party makes it easier
for law enforcement: “Third parties increase the probability that a trail will be left or witnesses will be created, all of which only helps the state in building its
case.” Ibid. By deterring criminals from relying on
third parties in the first place, the third-party doctrine’s applicability to lawful contractual arrangements may sometimes make it more difficult to detect
crime, not less. By contrast, if the third-party doctrine
were narrowed, although it may be necessary to get a
warrant to obtain evidence in the possession of a third
party, “that is not a particularly high standard to
meet.” Ibid. Finally, a grand jury subpoena duces tecum could continue to be supported by something less
than probable cause. Ibid.; see United States v. Dionisio, 410 U.S. 1, 11-12 (1973) (“The Fourth Amendment provides protection against a grand jury subpoena duces tecum too sweeping in its terms ‘to be regarded as reasonable.’ ” (quoting Hale v. Henkel, 201
U.S. 43, 76 (1906))); Carpenter, 585 U.S. at 362 (Alito,
J., dissenting) (suggesting “upheaval” will result if
“every grand jury subpoena duces tecum [must] be
supported by probable cause”). In short, the notion
that the Fourth Amendment must be dispensed with
in the context of third-party contracts to allow law enforcement to do their job is difficult to credit.
To commit a crime means, concretely, to initiate
force or use fraud against another person or another’s
property. No matter how one does this, some trail of
evidence will exist. Yes, without as broad a thirdparty doctrine, a warrant may be required to learn, for
example, the identity of the person whose IP address
is linked to an online theft from a bank account. However, given the occurrence of a theft, and knowledge of
which IP address was involved, that warrant should
10
not be difficult to get. Moreover, as amicus X Corp.
has argued, even without the third-party doctrine,
government can use undercover agents to investigate
criminal activity without violating the Fourth Amendment. See Br. of X Corp. as Amicus Curiae in Supp. of
Pet’r at 15 (citing Peikoff, supra, at 374-76).
Kerr’s second defense of the doctrine was based on
the need for ex ante clarity, given the high stakes of
the exclusionary rule’s evidence-suppression remedy.
Kerr 2009, supra, at 582. See also Issacharoff &
Wirshba, supra, at 987 (“The third party doctrine has
the virtue of simplicity and administrability.”). Justice Gorsuch has, like Kerr, expressed a desire for a
solution that provides ex ante clarity in the application of the Fourth Amendment, but not one that
makes it so “the king always wins” or the “king always
loses.” Carpenter, 585 U.S. at 390 (Gorsuch, J., dissenting).
What amicus X Corp. suggests offers exactly the solution Justice Gorsuch desires: whenever legally enforceable terms of service that provide for the confidentiality of user information are in place, those terms
should be respected and a warrant based on probable
cause should usually be obtained before government
gains access to the information held by the service provider. X Corp. is not suggesting that terms of service
must (or would) always include such privacy-protective terms. Nor is X Corp. suggesting that courts impute such terms when they are absent—particularly
when the terms of service state, for example, that a
provider may share a user’s information with law enforcement, which is often the case. In the absence of
privacy-protective terms, no warrant would be required for government to obtain the information from
the service provider. Such a rule would both be easy
11
to apply and accord with users’ actual expectations of
privacy, because users’ expectations would reflect the
privacy arrangements to which they actually agreed.
In sum, normative arguments for the third-party
doctrine—whether based on “technological neutrality”
or ex ante clarity—are not persuasive.
III. Recasting the Third-Party Doctrine as
“Consent” or “Disclosure” Only Raises More
Questions
The third-party doctrine suffers, not only from a
lack of normative justification, but also from a lack of
plausibility. It is highly counterintuitive to think
that, simply by sharing information with a thirdparty, even if subject to agreed-upon, stringent privacy protections, we have relinquished a “reasonable
expectation of privacy” in it. It is to address this lack
of plausibility that Kerr attempted to recast the doctrine in terms of “consent.” Kerr 2009, supra, at 587.
He argued that, in United States v. White, 401 U.S.
745 (1971), Justice White “chose the wrong doctrinal
prong. Instead of grounding the doctrine in consent
principles, he reasoned that use of a secret agent did
not violate a reasonable expectation of privacy.” Kerr
2009, supra, at 589 (footnotes omitted). In other
words, even if one’s expectation of privacy in the information shared with third parties is reasonable, so is a
consented-to search, and this, Kerr argued, is what
you have in the third-party situation.
Epstein challenged this recasting of the doctrine:
To be sure, there are many cases where
the consent of the party searched meets
the standard of individualized consent
developed in private law settings. But in
12
other cases the nominal consent is presumed on the ground that on balance
people are better off from the ex ante perspective if they are forced to submit to
some searches against their will.
Epstein, supra, at 1206; see also Carpenter, 585 U.S.
at 390 (Gorsuch, J., dissenting) (“Consenting to give a
third party access to private papers that remain my
property is not the same thing as consenting to a
search of those papers by the government.”); Murphy,
supra, at 1241 n.6 (agreeing that the “ ‘consent’ model
seems to just circle back to the reasonable expectation
of privacy test.”).
In his 2025 book, Kerr further develops his defense
of the third-party doctrine by recasting it in a different
way. He no longer grounds the doctrine in consent;
instead, he argues it is an instance of the “disclosure
rule,” which says, in the third-party context, “you have
no reasonable expectation of privacy in what you voluntarily disclose to third parties.” Kerr 2025, supra,
at 147. Kerr writes:
[T]he third-party doctrine is a sensible
rule that was accidentally mislabeled.
It’s really just the traditional idea, going
back to the Supreme Court’s first major
search-and-seizure case in 1878, Ex
parte Jackson, that concealment is
needed to establish Fourth Amendment
protection. That makes sense, at least in
a lot of cases. When you share information with someone, it becomes their
information, too. They can do with it as
they please without violating your
Fourth Amendment rights. Of course,
13
we can debate how far to take this principle. . . . But the foundations of the
third-party doctrine have been around in
the physical world for about as long as
courts have been interpreting the Fourth
Amendment.
Ibid. There is a lot to unpack. First, does something
qualify as a principle when it is unclear how far it
should be taken, when it “makes sense” only in “a lot
of cases”? Second, given that the Fourth Amendment
is a constraint on government, does it matter that a
private “third party” would not violate your Fourth
Amendment rights by doing as he or she pleases with
your information? For example, people may also be
censored by private third parties such as social media
platforms. That does not mean the government may
constitutionally censor them as well. Similarly here,
while sharing information with third parties pursuant
to a confidentiality agreement does not preclude the
third party from breaching that agreement consistent
with the Fourth Amendment, that certainly does not
imply the government may constitutionally demand
access to that information as well.
Leaving aside these flaws in Kerr’s reasoning,
Kerr’s reliance upon Ex parte Jackson, 96 U.S. 727
(1877), as the foundation for the third-party doctrine
is misplaced. Kerr relies upon Jackson, not only as
support for the doctrine, but more generally as support for a “content/non-content distinction”—the idea
that only the content of communications should be
protected by the Fourth Amendment’s warrant requirement; “non-content” or “metadata” should not receive such protection. See Kerr 2025, supra, at 139.
14
Such a distinction would itself require substantially narrowing the scope of the third-party doctrine
in its current form, as one can of course share both
content and non-content with third parties. In any
event, however, Kerr’s argument for the content/noncontent distinction starts with the premise that communications conducted remotely, by telephone or computer network, should receive the same protection
from government observation as communications via
in-person meeting. Just as the government could observe you leaving your home, traveling to another’s
home, entering to have a conversation, and later returning home, Kerr argues, government should be
able to learn, without a warrant, that you sent a communication, something about its length, what time
you sent it, to whom you sent it, etc. And similarly for
phone calls—who placed the call, to whom, when, for
how long, etc. Id. at 137-38.
Why should courts provide identical protection in
these scenarios? Why shouldn’t protection be provided according to an individual’s lawful exercise of
his or her common-law rights? Kerr does not explain
why courts should “match protections between the
physical world and the networked world.” Kerr 2025,
supra, at 136. He says only, “If the goal is to match
protections between the physical meeting and the network communication,” then the way to do that is to
allow “the government [to] collect the network equivalent of what the officer saw in public surveillance in
the physical example” without a warrant. Id. at 138
(emphasis added). But contractual promises made by
today’s service providers make it possible for
metadata to be private. Why not make those promises
relevant to the Fourth Amendment protection
metadata receives? In Jones, Justice Scalia wrote, “At
15
bottom, we must ‘assur[e] preservation of that degree
of privacy against government that existed when the
Fourth Amendment was adopted.’ ” United States v.
Jones, 565 U.S. 400, 406 (2012) (quoting Kyllo v.
United States, 533 U.S. 27, 34 (2001)) (emphasis
added). The degree of privacy against government
that existed when the Fourth Amendment was
adopted was grounded in the common law, including
common law rights of contract. See Carpenter, 585
U.S. at 397 (Gorsuch, J., dissenting) (“[T]he traditional approach [to the Fourth Amendment] asked if a
house, paper or effect was yours under law.”); id. at
399 (quoting Joseph Story, Commentaries on the Law
of Bailments § 2, p. 2 (1832)) (“[A] bailment is a delivery of a thing in trust for some special object or purpose, and upon a contract, express or implied, to conform to the object or purpose of the trust.”) (emphasis
added).
Kerr’s reliance on Ex parte Jackson is misplaced.
In Jackson, this Court “announced the rules for postal
network surveillance.” Id. at 139. Justice Field distinguished “between different kinds of mail matter,—
between what is intended to be kept free from inspection, such as letters, and sealed packages subject to
letter postage; and what is open to inspection, such as
newspapers, magazines, pamphlets, and other printed
matter, purposely left in a condition to be examined.”
Jackson, 96 U.S. at 733. As to the former, “Letters
and sealed packages of this kind in the mail are as
fully guarded from examination and inspection, except
as to their outward form and weight, as if they were
retained by the parties forwarding them in their own
domiciles.” Ibid. (emphasis added). Kerr infers that
“outward form and weight” includes all postal
“metadata,” such as names, addresses, and date of
16
mailing, and chalks up Jackson as support for his content/non-content distinction. Kerr 2025, supra, at
140.
Suppose it is true that Justice Field meant that all
postal metadata was properly subject to warrantless
inspection by postal service officials. Even so, Field
might not insist that the same content/non-content
distinction applied to government postal service inspections must also be applied to private electronic
service providers that transport or transmit content
subject to confidentiality agreements. It is not at all
clear, for example, that a user’s expectation of privacy
in the “outward form and weight” of an envelope is the
same as his or her expectation of privacy in the identity of the recipient of an encrypted Signal message.
Caution about applying the same distinction in other
contexts is warranted because, as Kerr notes, “Ex
parte Jackson does not explain why it drew the lines
it did.” Kerr 2025, supra, at 140. See also Daniel J.
Solove, Data Is What Data Does: Regulating Based on
Harm and Risk Instead of Sensitive Data, 118 Nw.
Univ. L. Rev. 1081, 1116-18 (2024) (questioning the
value of the content/non-content distinction because
metadata can “enable[] highly sensitive inferences”
and “be very revealing”).
This brings us back to the problem with Kerr relying upon Jackson for “the foundations of the thirdparty doctrine.” Kerr 2025, supra, at 147. In Jackson
there is no “third party”: the “disclosure” is made by
a postal customer directly to government officials! See
also Carpenter, 585 U.S. at 332 (Kennedy, J., dissenting) (citing Jackson as limiting, rather than supporting, Miller and Smith).
17
Moreover, Kerr must still address the cases in
which he admits the doctrine does not “make sense.”
Ibid. Enter “equilibrium adjustment,” which Kerr describes as the establishment of new rules “away from
the content/metadata line,” rules made necessary because “technological change is allowing new and more
invasive surveillance on the outside/metadata side of
the line.” Kerr 2025, supra, at 148. It is in terms of
equilibrium adjustment that Kerr explains this
Court’s ruling in Carpenter: “New technology [cell
sites recording information about cell phones connected to them] had eliminated a reasonable expectation of privacy. The law needed to restore it, adding
back the expectation of privacy that technology had
taken away.” Id. at 155. Of course, it is not the technology that had “eliminated a reasonable expectation
of privacy”; it is the third-party doctrine applied to
that technology. The same issue exists here. But this
is not the only issue with Kerr’s equilibrium adjustment theory.
Before showing how his theory applies to Carpenter, Kerr discusses this Court’s ruling in Jones. He
describes the Jones majority as “introducing a new
test: the installation of the GPS device was a search
because it was a trespass, regardless of whether its
subsequent use infringed on Jones’s reasonable expectation of privacy.” Kerr 2025, supra, at 149 (citing
Jones, 565 U.S. at 404) (emphasis added). He then
relies on language in Jones concurrences to characterize the case as an example of “classic equilibrium adjustment.” Kerr 2025, supra, at 149. However, as Justice Scalia noted, it is the Katz v. United States, 389
U.S. 347, 361 (1967), “reasonable expectation of privacy” test that was new—it “has been added to, not
substituted for, the common-law trespassory test.”
18
Jones, 565 U.S. at 409. Cf. Case v. Montana, 146 S. Ct.
500, 513 (2026) (Gorsuch, J., concurring) (“For a period, to be sure, the miasma created by this Court’s
Katz era led some to think the scope of the rights guaranteed by the Fourth Amendment depend on nothing
more than current judicial instincts about ‘reasonable
expectations of privacy.’ But that confusion cannot
last forever, for no one should think the rights of
Americans hang on so thin a thread. Instead, and as
Justice Story recognized, the Fourth Amendment is
made of sturdier stuff, representing ‘the affirmance of
a great constitutional doctrine of the common law.’ ”)
(internal citations omitted).
Kerr describes the “confusion” of lower courts, postCarpenter. “When applying the case to new facts,
lower courts often have focused on whether the facts
before them resemble those in Carpenter.” Kerr 2025,
supra, at 153. True enough, as the fractured reasoning in the en banc Fourth Circuit demonstrates. But
Kerr’s own theory suffers from the same issue with ex
ante clarity. In his discussion of the “privacies of life”
prong of his test, Kerr does little more than list examples of the sorts of things that judges have found to be
encompassed by this descriptor. See Kerr 2025, supra,
at 158-60. Better to adopt a clear test such as the one
X Corp. proposes here.
In a forthcoming article, Kerr applies his model to
reverse searches of databases, such as the geofence
warrant at issue in the instant case. Orin S. Kerr,
Data Scanning and the Fourth Amendment, 67 B.C. L.
Rev. 431 (2026) (forthcoming) (“Kerr 2026”). However, because his argument starts with the assumption that “data scans do not involve physical intrusion,” id. at 460, he fails to address arguments like
those made in this brief that scanning an account that
19
a service provider agreed to keep confidential is a
Fourth Amendment search, or that “the government,
via Google, searched every account” in its Sensorvault
at step one, making the geofence warrant a general
warrant, Pet’r’s Opening Br. at 34. Kerr argues that
what’s important in determining when a search of a
database occurs is when and how much information is
“revealed to human observation.” Kerr 2026, supra, at
443. “For a search to occur, information must be exposed to human observation.” Id. at 460. But per
Jones, trespass upon property, including one’s “papers” and “effects,” is a search, Jones, 565 U.S. at 411,
and under common law a trespass occurs when a person accesses, without consent, the property of another
(or causes an object or instrumentality to gain such
access). See, e.g., Restatement (Second) of Torts
§ 217(e) (1965).
Katz-ian balancing tests were supposed to fill in
gaps of privacy protection alleged to have been left by
the common law. But in recent decades they have often had the opposite effect and, moreover, have left individuals uncertain about what legal protection their
privacy will receive. If Kerr’s Katz-ian theory is
adopted, we will only see more of this.
IV. Coda: What about Katz?
Students of legal philosophy may recall Lon
Fuller’s The Case of the Speluncean Explorers, 62
Harv. L. Rev. 616 (1949). It was a set of fictitious legal
opinions, written in the year 4300 by Supreme Court
Justices of Newgarth, each of whom analyzed the case
before the Court using a different theory of jurisprudence. The question presented was whether to uphold
convictions for murder of speluncean (cave) explorers
20
who, after having been stranded for many days without food and, after participating in an (arguably)
agreed-upon casting of dice, exercised their “right” to
eat their fellow explorers. Id. at 616-19. This ghastly
and unique set of facts allowed for the opinions to each
be a paradigmatic example of a single jurisprudential
philosophy. The legal positivist/realist could say “law
is law” and chide his colleagues’ squeamishness. Id.
at 631-37. The natural law theorist could declare the
situation outside the jurisdiction of his laws and use
natural law principles to decide the explorers’ fates.
Id. at 620-26. The pragmatist could appeal to public
opinion polls. Id. at 637-44. And so on.
The set of opinions written by the en banc Fourth
Circuit in this case could be said to resemble The Case
of the Speluncean Explorers because, as Judge Gregory observed, “its reasoning is fractured.” Chatrie,
136 F.4th at 157 (Gregory, J., dissenting). Here, however, the “fractured reasoning” is due, not to any
judges disregarding the relevant precedent, but instead because that precedent is so amorphous, so flexible, that a judge’s reasoning could be influenced by
his or her individual ethical, political, and jurisprudential commitments, and still be within the bounds
of what a reasonable, conscientious judge would conclude in this case.
At one extreme, Judge Wilkinson wrote, “There
was no search because this case involved a straightforward application of [Miller and Smith].” Chatrie,
136 F.4th at 109 (Wilkinson, J., concurring) (citations
omitted). While he made a glancing reference to Carpenter’s balancing test, it did not seem to sway him in
the slightest. Wilkinson warned, “[P]rivacy is in part
a peace of mind. The prospect of criminal malefactors
intruding on that peace can only mean our privacy has
21
been compromised. That the transgression is attributable to private actors does not mean it cannot be
part of the calculus of reasonableness.” Id. at 110. He
referred to his colleagues’ arguments that geofence
warrants violate the Fourth Amendment as an “assault.” Id. at 109. While some share our Founders’
concerns about invasions of privacy by government,
Wilkinson wrote, “privacy is not invariably in an adversarial relationship with the state, but something
the state can take measured steps to protect and provide.” Id. at 110. But see United States v. Smith, 110
F.4th 817, 834 (5th Cir. 2024) (“Carpenter’s application to the third-party doctrine in this case is straightforward.”); id. at 836 (holding the third-party doctrine
does not apply to the geofence warrant at issue).
At the other extreme was Judge Wynn, who urged
that “the principles enshrined in the Fourth Amendment . . . . be vigorously protected from ever-expanding methods of government intrusion.” Chatrie, 136
F.4th at 115 (Wynn, J., concurring). See also id. at
117 (discussing the home intrusion in Kyllo and the
“traditional trespass principles” applied by Justice
Scalia in Jones); id. at 118 (discussing Riley’s treatment of an arrestee’s cell phone as an “effect” under
the Fourth Amendment). He rejected the view that
users who share information with service providers
like Google or X Corp. for a limited purpose thereby
relinquish their Fourth Amendment rights:
“Smartphone users might reasonably expect that
their deidentified data will be used, in aggregate, to
fine-tune targeted advertising. But it would be a
grave misjudgment to conflate an individual’s limited
disclosure to Google with an open invitation to the
state.” Id. at 127 (citations omitted).
22
Judge Richardson discussed the same “voluntariness” factors from Carpenter as Judge Wynn, id. at
138-39 (Richardson, J., concurring), but reached a different result. Whereas Wynn focused on the capacities of Location History to implicate privacy concerns,
id. at 126 (Wynn, J., concurring), Richardson focused
narrowly on the results of the geofence warrant at issue, noting “the two hours’ worth of Location History
data that law enforcement obtained from Google at
Step two” was “far less revealing than that obtained
in Jones, Carpenter, or Beautiful Struggle and more
like the short-term public movements in Knotts, which
the Court found were ‘voluntarily conveyed to anyone
who wanted to look.’ ” Id. at 139 (Richardson, J., concurring) (citations omitted). In addition, Richardson
found, contra Wynn, that “a user knowingly and voluntarily exposes his Location History data to Google.”
Id. at 140. “The third-party doctrine,” he concluded,
“squarely governs this case.” Id. at 141.
Judge Berner also applied the Carpenter majority’s
balancing tests, but she analyzed the three steps of
the Google geofence warrant process separately in
terms of an additional factor: whether the information produced was “likely to be traceable to the
identities of particular Google users.” Id. at 143
(Berner, J., concurring). Only if it was traceable to
individual users’ identities, she argued, was the users’
reasonable expectation of privacy in their Location
Histories impacted under Carpenter. Id. at 144. But
see supra pp. 18-19 (showing that even step one of the
geofence warrant effected a trespass on user data and
therefore should require a proper warrant). Berner
disagreed with the Fifth Circuit’s holding in Smith
that geofence warrants were categorically unconstitu-
23
tional, Chatrie, 136 F.4th at 144 (Berner, J., concurring), but found the geofence warrant in this case was
unconstitutional because it lacked probable cause. Id.
at 153 (“A person’s mere proximity to suspected criminal activity ‘does not, without more, give rise to probable cause to search that person.’ ”) (citation omitted).
Judge Gregory agreed with Judges Wynn and
Berner that the geofence warrant violated the Fourth
Amendment under Carpenter. Id. at 157 (Gregory, J.,
dissenting). Unlike them, however, he found that conclusion so obvious, he would have excluded the evidence against Petitioner Chatrie: “[A]n officer need
not know the judiciary’s view on the use of new technology with the Fourth Amendment to know that the
information in the warrant was insufficient.” Id. at
160.
As these varied opinions demonstrate, the amorphous quality of the Katz and Carpenter balancing
tests allow judges and scholars to read into the various factors other values and normative commitments,
including them among the demands to be weighed.
See also Carpenter, 585 U.S. at 343 (Thomas, J., dissenting) (“[The Katz test] invites courts to make judgments about policy, not law.”); id. at 357-58 (“Even
Justice Harlan, four years after penning his concurrence in Katz, confessed that the test encouraged ‘the
substitution of words for analysis.’ ” (citing White, 401
U.S. at 745 (Harlan, J., dissenting)); id. at 393-94
(Gorsuch, J., dissenting) (“When judges abandon legal
judgment for political will we . . . risk decisions where
‘reasonable expectations of privacy’ come to bear ‘an
uncanny resemblance to those expectations of privacy’
shared by Members of this Court.” (quoting Minnesota
v. Carter, 525 U.S. 83, 97 (1998) (Scalia, J., concurring))).
24
The third-party doctrine of Miller and Smith, like
any legal doctrine that is put through a Katz-ian filter,
necessarily lacks ex ante clarity. Most importantly, as
in the instant case, balancing demands for “anything
under the sun,” William James, The Moral Philosopher and Moral Life, in The Will to Believe and Other
Essays in Popular Philosophy 201 (1956), often violates individual rights, the protection of which is a
non-negotiable demand of a constitutional republic. 5
CONCLUSION
The Court-created Katz test was “added to, not substituted for, the common law trespassory test.” Jones,
565 U.S. at 409. If Justice Scalia were on this Court
in 1967 to pen a majority opinion in Katz, everyone
reading this brief might have better things to do. See
Kyllo, 533 U.S. at 40 (holding unlawful search occurred when Thermovision imaging used to effect an
intrusion into a home). The Katz test was intended to
afford us more privacy; it was to be applied in cases in
which the common law appeared too stingy. Now,
thanks to the Katz-mediated expansion of the thirdparty doctrine in Miller and Smith, individuals lawfully exercise their common-law rights, intending and
expecting their property rights and privacy to be protected, only to be told by courts that their expectations
are not “reasonable.” See Carpenter, 585 U.S. at 39495 (Gorsuch, J., dissenting) (collecting “unbelievable”
The history of the “right to privacy” has shown that laws
directed specifically at invasions of privacy tend, in their
application and proliferation, to erode fundamental rights to
liberty and property. See Amy L. Peikoff, Beyond Reductionism:
Reconsidering the Right to Privacy, 3 N.Y.U. J.L. & Liberty 1, 2445 (2008).
5
25
cases in which courts rejected as unreasonable, expectations of privacy based on common-law rights).
This Court can fix this. For all the reasons stated
in its briefing, amicus X Corp. urges this Court to find
that the Government violated Petitioner Chatrie’s
Fourth Amendment rights—along with those of other
Google users—when it obtained their Location Histories by means of a geofence warrant devoid of individualized suspicion. In so doing, this Court should, at
the very least, continue to narrow or distinguish Miller and Smith from cases in which, as here, enforceable, privacy-protective terms of service are in place,
and the user has asserted a right to exclude based on
these terms. See Pet’r’s Opening Br. at 15-16. This
would allow individuals to decide for themselves what
are “privacies of life” and what are not, and to exercise
their common-law rights to liberty, property, and contract, accordingly. 6 Courts would be left with the relatively straightforward task of deciding whether an
individual had exercised his or her right as necessary
to protect a state of privacy against warrantless, suspicionless searches.
Allowing individuals to protect their privacy in this
way would create market incentives for service providers to offer privacy-protective terms of service
where none currently exist. Enforcing such terms
would reduce barriers to offering more innovative uses
of sensitive data that ultimately benefit society, and
would also benefit law enforcement by reducing service providers’ incentive to employ drastic methods—
6 In those rare cases in which no common-law right has been or
conceivably could be exercised to protect against a government
agent’s unreasonable search or seizure, clearly defined limitations on government power are called for.
26
such as end-to-end encryption, which Google has now
implemented for Location History—that make it so,
even with a proper, particularized warrant, third parties hold no data to be searched.
Respectfully submitted,
AMY P EIKOFF
Pacific Legal Foundation
3100 Clarendon Blvd.,
Suite 1000
Arlington, VA 22201
(202) 888-6881
apeikoff@pacificlegal.org
MARK MILLER
Counsel of Record
Pacific Legal Foundation
4440 PGA Blvd.,
Suite 307
Palm Beach Gardens, FL
33410
(561) 691-5000
mark@pacificlegal.org
Counsel for Amicus Curiae X Corp.
M ARCH 2026
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