Carpenter v. United States

JUSTICE GORSUCH, dissenting.¶

In the late 1960s this Court suggested for the first time that a search triggering the Fourth Amendment occurs when the government violates an “expectation of privacy” that “society is prepared to recognize as ‘reasonable.'' Katz v. United States , 389 U. S. 347, 361 (1967) (Harlan, J., concurring). Then, in a pair of decisions in the 1970s applying the Katz test, the Court held that a “reasonable expectation of privacy” doesn’t attach to information shared with “third parties.” See Smith v. Maryland , 442 U. S. 735, 743–744 (1979); United States v. Miller , 425 U. S. 435, 443 (1976). By these steps, the Court came to conclude, the Constitution does nothing to limit investigators from searching records you’ve entrusted to your bank, accountant, and maybe even your doctor.¶

What’s left of the Fourth Amendment? Today we use the Internet to do most everything. Smartphones make it easy to keep a calendar, correspond with friends, make calls, conduct banking, and even watch the game. Countless Internet companies maintain records about us and, increasingly, for us. Even our most private documentsthose that, in other eras, we would have locked safely in a desk drawer or destroyed—now reside on third party servers. Smith and Miller teach that the police can review all of this material, on the theory that no one reasonably expects any of it will be kept private. But no one believes that, if they ever did.¶

What to do? It seems to me we could respond in at least three ways. The first is to ignore the problem, maintain Smith and Miller , and live with the consequences. If the confluence of these decisions and modern technology means our Fourth Amendment rights are reduced to nearly nothing, so be it. The second choice is to set Smith and Miller aside and try again using the Katz “reasonable expectation of privacy” jurisprudence that produced them. The third is to look for answers elsewhere.¶

*¶

Start with the first option. Smith held that the government’s use of a pen register to record the numbers people dial on their phones doesn’t infringe a reasonable expectation of privacy because that information is freely disclosed to the third party phone company. 442 U. S., at 743–744. Miller held that a bank account holder enjoys no reasonable expectation of privacy in the bank’s records of his account activity. That’s true, the Court reasoned, “even if the information is revealed on the assumption that it will be used only for a limited purpose and the confidence placed in the third party will not be betrayed.” 425 U. S., at 443. Today the Court suggests that Smith and Miller distinguish between kinds of information disclosed to third parties and require courts to decide whether to “extend” those decisions to particular classes of information, depending on their sensitivity. See ante, at 10–18. But as the Sixth Circuit recognized and JUSTICE KENNEDY explains, no balancing test of this kind can be found in Smith and Miller . See ante , at 16 (dissenting opinion). Those cases announced a categorical rule: Once you disclose information to third parties, you forfeit any reasonable expectation of privacy you might have had in it. And even if Smith and Miller did permit courts to conduct a balancing contest of the kind the Court now suggests, it’s still hard to see how that would help the petitioner in this case. Why is someone’s location when using a phone so much more sensitive than who he was talking to ( Smith ) or what financial transactions he engaged in ( Miller )? I do not know and the Court does not say.¶

The problem isn’t with the Sixth Circuit’s application of Smith and Miller but with the cases themselves. Can the government demand a copy of all your e-mails from Google or Microsoft without implicating your Fourth Amendment rights? Can it secure your DNA from 23andMe without a warrant or probable cause? Smith and Miller say yes it can—at least without running afoul of Katz . But that result strikes most lawyers and judges today—me included—as pretty unlikely. In the years since its adoption, countless scholars, too, have come to conclude that the “third-party doctrine is not only wrong, but horribly wrong.” Kerr, The Case for the Third-Party Doctrine, 107 Mich. L. Rev. 561, 563, n. 5, 564 (2009) (collecting criticisms but defending the doctrine (footnotes omitted)). The reasons are obvious. “As an empirical statement about subjective expectations of privacy,” the doctrine is “quite dubious.” Baude & Stern, The Positive Law Model of the Fourth Amendment, 129 Harv. L. Rev. 1821, 1872 (2016). People often do reasonably expect that information they entrust to third parties, especially information subject to confidentiality agreements, will be kept private. Meanwhile, if the third party doctrine is supposed to represent a normative assessment of when a person should expect privacy, the notion that the answer might be “never” seems a pretty unattractive societal prescription. Ibid.¶

What, then, is the explanation for our third party doctrine? The truth is, the Court has never offered a persuasive justification. The Court has said that by conveying information to a third party you ''assum[e] the risk'' it will be revealed to the police and therefore lack a reasonable expectation of privacy in it. Smith , supra, at 744. But assumption of risk doctrine developed in tort law. It generally applies when “by contract or otherwise [one] expressly agrees to accept a risk of harm” or impliedly does so by “manifest[ing] his willingness to accept” that risk and thereby “take[s] his chances as to harm which may result from it.” Restatement (Second) of Torts §§496B, 496C(1), and Comment b (1965); see also 1 D. Dobbs, P. Hayden, & E. Bublick, Law of Torts §§235–236, pp. 841–850 (2d ed. 2017). That rationale has little play in this context. Suppose I entrust a friend with a letter and he promises to keep it secret until he delivers it to an intended recipient. In what sense have I agreed to bear the risk that he will turn around, break his promise, and spill its contents to someone else? More confusing still, what have I done to “manifest my willingness to accept” the risk that the government will pry the document from my friend and read it without his consent?¶

One possible answer concerns knowledge. I know that my friend might break his promise, or that the government might have some reason to search the papers in his possession. But knowing about a risk doesn’t mean you assume responsibility for it. Whenever you walk down the sidewalk you know a car may negligently or recklessly veer off and hit you, but that hardly means you accept the consequences and absolve the driver of any damage he may do to you. Epstein, Privacy and the Third Hand: Lessons From the Common Law of Reasonable Expectations, 24 Berkeley Tech. L. J. 1199, 1204 (2009); see W. Keeton, D. Dobbs, R. Keeton, & D. Owen, Prosser & Keeton on Law of Torts 490 (5th ed. 1984).¶

Some have suggested the third party doctrine is better understood to rest on consent than assumption of risk. “So long as a person knows that they are disclosing information to a third party,” the argument goes, “their choice to do so is voluntary and the consent valid.” Kerr, supra, at 588. I confess I still don’t see it. 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. Perhaps there are exceptions, like when the third party is an undercover government agent. See Murphy, The Case Against the Case Against the Third-Party Doctrine: A Response to Epstein and Kerr, 24 Berkeley Tech. L. J. 1239, 1252 (2009); cf. Hoffa v. United States , 385 U. S. 293 (1966). But otherwise this conception of consent appears to be just assumption of risk relabeled—you’ve “consented” to whatever risks are foreseeable.¶

Another justification sometimes offered for third party doctrine is clarity. You (and the police) know exactly how much protection you have in information confided to others: none. As rules go, “the king always wins” is admirably clear. But the opposite rule would be clear too: Third party disclosures never diminish Fourth Amendment protection (call it “the king always loses”). So clarity alone cannot justify the third party doctrine.¶

In the end, what do Smith and Miller add up to? A doubtful application of Katz that lets the government search almost whatever it wants whenever it wants. The Sixth Circuit had to follow that rule and faithfully did just that, but it’s not clear why we should.¶

*¶

There’s a second option. What if we dropped Smith and Miller ’s third party doctrine and retreated to the root Katz question whether there is a “reasonable expectation of privacy” in data held by third parties? Rather than solve the problem with the third party doctrine, I worry this option only risks returning us to its source: After all, it was Katz that produced Smith and Miller in the first place.¶

Katz’s problems start with the text and original understanding of the Fourth Amendment, as JUSTICE THOMAS thoughtfully explains today. Ante, at 5–17 (dissenting opinion). The Amendment’s protections do not depend on the breach of some abstract “expectation of privacy” whose contours are left to the judicial imagination. Much more concretely, it protects your “person,” and your “houses, papers, and effects.” Nor does your right to bring a Fourth Amendment claim depend on whether a judge happens to agree that your subjective expectation to privacy is a “reasonable” one. Under its plain terms, the Amendment grants you the right to invoke its guarantees whenever one of your protected things (your person, your house, your papers, or your effects) is unreasonably searched or seized. Period.¶

History too holds problems for Katz . Little like it can be found in the law that led to the adoption of the Fourth Amendment or in this Court’s jurisprudence until the late 1960s. The Fourth Amendment came about in response to a trio of 18th century cases “well known to the men who wrote and ratified the Bill of Rights, [and] famous throughout the colonial population.” Stuntz, The Substantive Origins of Criminal Procedure, 105 Yale L. J. 393, 397 (1995). The first two were English cases invalidating the Crown’s use of general warrants to enter homes and search papers. Entick v. Carrington , 19 How. St. Tr. 1029 (K. B. 1765); Wilkes v. Wood , 19 How. St. Tr. 1153 (K. B. 1763); see W. Cuddihy, The Fourth Amendment: Origins and Original Meaning 439–487 (2009); Boyd v. United States , 116 U. S. 616, 625–630 (1886). The third was American: the Boston Writs of Assistance Case, which sparked colonial outrage at the use of writs permitting government agents to enter houses and business, breaking open doors and chests along the way, to conduct searches and seizures—and to force third parties to help them. Stuntz, supra, at 404–409; M. Smith, The Writs of Assistance Case (1978). No doubt the colonial outrage engendered by these cases rested in part on the government’s intrusion upon privacy. But the framers chose not to protect privacy in some ethereal way dependent on judicial intuitions. They chose instead to protect privacy in particular places and things—“persons, houses, papers, and effects”—and against particular threats—“unreasonable” governmental “searches and seizures.” See Entick , supra, at 1066 (“Papers are the owner’s goods and chattels; they are his dearest property; and so far from enduring a seizure, that they will hardly bear an inspection”); see also ante, at 1–21 (THOMAS, J., dissenting).¶

Even taken on its own terms, Katz has never been sufficiently justified. In fact, we still don’t even know what its “reasonable expectation of privacy” test is . Is it supposed to pose an empirical question (what privacy expectations do people actually have) or a normative one (what expectations should they have)? Either way brings problems. If the test is supposed to be an empirical one, it’s unclear why judges rather than legislators should conduct it. Legislators are responsive to their constituents and have institutional resources designed to help them discern and enact majoritarian preferences. Politically insulated judges come armed with only the attorneys’ briefs, a few law clerks, and their own idiosyncratic experiences. They are hardly the representative group you’d expect (or want) to be making empirical judgments for hundreds of millions of people. Unsurprisingly, too, judicial judgments often fail to reflect public views. See Slobogin & Schumacher, Reasonable Expectations of Privacy and Autonomy in Fourth Amendment Cases: An Empirical Look at “Understandings Recognized and Permitted by Society,” 42 Duke L. J. 727, 732, 740–742 (1993). Consider just one example. Our cases insist that the seriousness of the offense being investigated does not reduce Fourth Amendment protection. Mincey v. Arizona , 437 U. S. 385, 393–394 (1978). Yet scholars suggest that most people are more tolerant of police intrusions when they investigate more serious crimes. See Blumenthal, Adya, & Mogle, The Multiple Dimensions of Privacy: Testing Lay “Expectations of Privacy,” 11 U. Pa. J. Const. L. 331, 352–353 (2009). And I very much doubt that this Court would be willing to adjust its Katz cases to reflect these findings even if it believed them.¶

Maybe, then, the Katz test should be conceived as a normative question. But if that’s the case, why (again) do judges, rather than legislators, get to determine whether society should be prepared to recognize an expectation of privacy as legitimate? Deciding what privacy interests should be recognized often calls for a pure policy choice, many times between incommensurable goods—between the value of privacy in a particular setting and society’s interest in combating crime. Answering questions like that calls for the exercise of raw political will belonging to legislatures, not the legal judgment proper to courts. See The Federalist No. 78, p. 465 (C. Rossiter ed. 1961) (A. Hamilton). When judges abandon legal judgment for political will we not only risk decisions where “reasonable expectations of privacy” come to bear “an uncanny resemblance to those expectations of privacy” shared by Members of this Court. Minnesota v. Carter , 525 U. S. 83, 97 (1998) (Scalia, J., concurring). We also risk undermining public confidence in the courts themselves.¶

My concerns about Katz come with a caveat. Sometimes , I accept, judges may be able to discern and describe existing societal norms. See, e.g., Florida v. Jardines , 569 U. S. 1, 8 (2013) (inferring a license to enter on private property from the ''habits of the country'' (quoting McKee v. Gratz , 260 U. S. 127, 136 (1922))); Sachs, Finding Law, 107 Cal. L. Rev. (forthcoming 2019), online at https://ssrn.com/ abstract=3064443 (as last visited June 19, 2018). That is particularly true when the judge looks to positive law rather than intuition for guidance on social norms. See¶

Byrd v. United States, 584 U. S. ___, ___–___ (2018) (slip op., at 7–9) (“general property-based concept[s] guid[e] the resolution of this case”). So there may be some occasions where Katz is capable of principled application—though it may simply wind up approximating the more traditional option I will discuss in a moment. Sometimes it may also be possible to apply Katz by analogizing from precedent when the line between an existing case and a new fact pattern is short and direct. But so far this Court has declined to tie itself to any significant restraints like these. See ante, at 5, n. 1 (“[W]hile property rights are often informative, our cases by no means suggest that such an interest is ‘fundamental’ or ‘dispositive’ in determining which expectations of privacy are legitimate”).¶

As a result, Katz has yielded an often unpredictableand sometimes unbelievable—jurisprudence. Smith and Miller are only two examples; there are many others. Take Florida v. Riley , 488 U. S. 445 (1989), which says that a police helicopter hovering 400 feet above a person’s property invades no reasonable expectation of privacy. Try that one out on your neighbors. Or California v. Greenwood , 486 U. S. 35 (1988), which holds that a person has no reasonable expectation of privacy in the garbage he puts out for collection. In that case, the Court said that the homeowners forfeited their privacy interests because “[i]t is common knowledge that plastic garbage bags left on or at the side of a public street are readily accessible to animals, children, scavengers, snoops, and other members of the public.” Id. , at 40 (footnotes omitted). But the habits of raccoons don’t prove much about the habits of the country. I doubt, too, that most people spotting a neighbor rummaging through their garbage would think they lacked reasonable grounds to confront the rummager. Making the decision all the stranger, California state law expressly protected a homeowner’s property rights in discarded trash. Id. , at 43. Yet rather than defer to that as evidence of the people’s habits and reasonable expectations of privacy, the Court substituted its own curious judgment.¶

Resorting to Katz in data privacy cases threatens more of the same. Just consider. The Court today says that judges should use Katz ’s reasonable expectation of privacy test to decide what Fourth Amendment rights people have in cell-site location information, explaining that “no single rubric definitively resolves which expectations of privacy are entitled to protection.” Ante, at 5. But then it offers a twist. Lower courts should be sure to add two special principles to their Katz calculus: the need to avoid “arbitrary power” and the importance of “plac[ing] obstacles in the way of a too permeating police surveillance.” Ante, at 6 (internal quotation marks omitted). While surely laudable, these principles don’t offer lower courts much guidance. The Court does not tell us, for example, how far to carry either principle or how to weigh them against the legitimate needs of law enforcement. At what point does access to electronic data amount to “arbitrary” authority? When does police surveillance become “too permeating”? And what sort of “obstacles” should judges “place” in law enforcement’s path when it does? We simply do not know.¶

The Court’s application of these principles supplies little more direction. The Court declines to say whether there is any sufficiently limited period of time “for which the Government may obtain an individual’s historical [location information] free from Fourth Amendment scrutiny.” Ante, at 11, n. 3; see ante, at 11–15. But then it tells us that access to seven days’ worth of information does trigger Fourth Amendment scrutiny—even though here the carrier “produced only two days of records.” Ante, at 11, n. 3 . Why is the relevant fact the seven days of information the government asked for instead of the two days of information the government actually saw ? Why seven days instead of ten or three or one? And in what possible sense did the government “search” five days’ worth of location information it was never even sent? We do not know.¶

Later still, the Court adds that it can’t say whether the Fourth Amendment is triggered when the government collects “real-time CSLI or ‘tower dumps’ (a download of information on all the devices that connected to a particular cell site during a particular interval).” Ante, at 17–18. But what distinguishes historical data from real-time data, or seven days of a single person’s data from a download of everyone ’s data over some indefinite period of time? Why isn’t a tower dump the paradigmatic example of “too permeating police surveillance” and a dangerous tool of “arbitrary” authority—the touchstones of the majority’s modified Katz analysis? On what possible basis could such mass data collection survive the Court’s test while collecting a single person’s data does not? Here again we are left to guess. At the same time, though, the Court offers some firm assurances. It tells us its decision does not “call into question conventional surveillance techniques and tools, such as security cameras.” Ibid. That, however, just raises more questions for lower courts to sort out about what techniques qualify as “conventional” and why those techniques would be okay even if they lead to “permeating police surveillance” or “arbitrary police power.”¶

Nor is this the end of it. After finding a reasonable expectation of privacy, the Court says there’s still more work to do. Courts must determine whether to “extend” Smith and Miller to the circumstances before them. Ante, at 11, 15–17. So apparently Smith and Miller aren’t quite left for dead; they just no longer have the clear reach they once did. How do we measure their new reach? The Court says courts now must conduct a second Katz -like balancing inquiry, asking whether the fact of disclosure to a third party outweighs privacy interests in the “category of information” so disclosed. Ante, at 13, 15–16. But how are lower courts supposed to weigh these radically different interests? Or assign values to different categories of information? All we know is that historical cell-site location information (for seven days, anyway) escapes Smith and Miller ’s shorn grasp, while a lifetime of bank or phone records does not. As to any other kind of information, lower courts will have to stay tuned.¶

In the end, our lower court colleagues are left with two amorphous balancing tests, a series of weighty and incommensurable principles to consider in them, and a few illustrative examples that seem little more than the product of judicial intuition. In the Court’s defense, though, we have arrived at this strange place not because the Court has misunderstood Katz . Far from it. We have arrived here because this is where Katz inevitably leads.¶

*¶

There is another way. From the founding until the 1960s, the right to assert a Fourth Amendment claim didn’t depend on your ability to appeal to a judge’s personal sensibilities about the “reasonableness” of your expectations or privacy. It was tied to the law. Jardines , 569 U. S., at 11; United States v. Jones , 565 U. S. 400, 405 (2012). The Fourth Amendment protects “the right of the people to be secure in their persons, houses, papers and effects, against unreasonable searches and seizures.” True to those words and their original understanding, the traditional approach asked if a house, paper or effect was yours under law. No more was needed to trigger the Fourth Amendment. Though now often lost in Katz ’s shadow, this traditional understanding persists. Katz only “supplements, rather than displaces the traditional propertybased understanding of the Fourth Amendment.” Byrd , 584 U. S., at ___ (slip op., at 7) (internal quotation marks omitted); Jardines , supra, at 11 (same); Soldal v. Cook County , 506 U. S. 56, 64 (1992) ( Katz did not “snuf[f] out the previously recognized protection for property under the Fourth Amendment”).¶

Beyond its provenance in the text and original understanding of the Amendment, this traditional approach comes with other advantages. Judges are supposed to decide cases based on “democratically legitimate sources of law”—like positive law or analogies to items protected by the enacted Constitution—rather than “their own biases or personal policy preferences.” Pettys, Judicial Discretion in Constitutional Cases, 26 J. L. & Pol. 123, 127 (2011). A Fourth Amendment model based on positive legal rights “carves out significant room for legislative participation in the Fourth Amendment context,” too, by asking judges to consult what the people’s representatives have to say about their rights. Baude & Stern, 129 Harv. L. Rev., at 1852. Nor is this approach hobbled by Smith and Miller , for those cases are just limitations on Katz , addressing only the question whether individuals have a reasonable expectation of privacy in materials they share with third parties. Under this more traditional approach, Fourth Amendment protections for your papers and effects do not automatically disappear just because you share them with third parties.¶

Given the prominence Katz has claimed in our doctrine, American courts are pretty rusty at applying the traditional approach to the Fourth Amendment. We know that if a house, paper, or effect is yours, you have a Fourth Amendment interest in its protection. But what kind of legal interest is sufficient to make something yours ? And what source of law determines that? Current positive law? The common law at 1791, extended by analogy to modern times? Both? See Byrd , supra , at ___–___ (slip op., at 1–2) (THOMAS, J., concurring); cf. Re, The Positive Law Floor, 129 Harv. L. Rev. Forum 313 (2016). Much work is needed to revitalize this area and answer these questions. I do not begin to claim all the answers today, but (unlike with Katz ) at least I have a pretty good idea what the questions are . And it seems to me a few things can be said.¶

First , the fact that a third party has access to or possession of your papers and effects does not necessarily eliminate your interest in them. Ever hand a private document to a friend to be returned? Toss your keys to a valet at a restaurant? Ask your neighbor to look after your dog while you travel? You would not expect the friend to share the document with others; the valet to lend your car to his buddy; or the neighbor to put Fido up for adoption. Entrusting your stuff to others is a bailment . A bailment is the “delivery of personal property by one person (the bailor ) to another (the bailee ) who holds the property for a certain purpose.” Black’s Law Dictionary 169 (10th ed. 2014); J. 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, expressed or implied, to conform to the object or purpose of the trust”). A bailee normally owes a legal duty to keep the item safe, according to the terms of the parties’ contract if they have one, and according to the “implication[s] from their conduct” if they don’t. 8 C. J. S., Bailments §36, pp. 468–469 (2017). A bailee who uses the item in a different way than he’s supposed to, or against the bailor’s instructions, is liable for conversion. Id. , §43, at 481; see Goad v. Harris , 207 Ala. 357, 92 So. 546, (1922); Knight v. Seney , 290 Ill. 11, 17, 124 N. E. 813, 815–816 (1919); Baxter v. Woodward , 191 Mich. 379, 385, 158 N. W. 137, 139 (1916). This approach is quite different from Smith and Miller ’s (counter)-intuitive approach to reasonable expectations of privacy; where those cases extinguish Fourth Amendment interests once records are given to a third party, property law may preserve them.¶

Our Fourth Amendment jurisprudence already reflects this truth. In Ex parte Jackson , 96 U. S. 727 (1878), this Court held that sealed letters placed 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.” Id., at 733. The reason, drawn from the Fourth Amendment’s text, was that “[t]he constitutional guaranty of the right of the people to be secure in their papers against unreasonable searches and seizures extends to their papers , thus closed against inspection, wherever they may be .” Ibid. (emphasis added). It did not matter that letters were bailed to a third party (the government, no less). The sender enjoyed the same Fourth Amendment protection as he does “when papers are subjected to search in one’s own household.” Ibid.¶

These ancient principles may help us address modern data cases too. Just because you entrust your data—in some cases, your modern-day papers and effects—to a third party may not mean you lose any Fourth Amendment interest in its contents. Whatever may be left of Smith and Miller , few doubt that e-mail should be treated much like the traditional mail it has largely supplantedas a bailment in which the owner retains a vital and protected legal interest. See ante, at 13 (KENNEDY, J., dissenting) (noting that enhanced Fourth Amendment protection may apply when the “modern-day equivalents of an individual’s own ‘papers’ or ‘effects’ . . . are held by a third party” through “bailment”); ante, at 23, n. 6 (ALITO, J., dissenting) (reserving the question whether Fourth Amendment protection may apply in the case of “bailment” or when “someone has entrusted papers he or she owns . . . to the safekeeping of another”); United States v. Warshak , 631 F. 3d 266, 285–286 (CA6 2010) (relying on an analogy to Jackson to extend Fourth Amendment protection to e-mail held by a third party service provider).¶

Second , I doubt that complete ownership or exclusive control of property is always a necessary condition to the assertion of a Fourth Amendment right. Where houses are concerned, for example, individuals can enjoy Fourth Amendment protection without fee simple title. Both the text of the Amendment and the common law rule support that conclusion. “People call a house ‘their’ home when legal title is in the bank, when they rent it, and even when they merely occupy it rent free.” Carter , 525 U. S., at 9596 (Scalia, J., concurring). That rule derives from the common law. Oystead v. Shed , 13 Mass. 520, 523 (1816) (explaining, citing “[t]he very learned judges, Foster , Hale , and Coke ,” that the law “would be as much disturbed by a forcible entry to arrest a boarder or a servant, who had acquired, by contract, express or implied, a right to enter the house at all times, and to remain in it as long as they please, as if the object were to arrest the master of the house or his children”). That is why tenants and resident family members—though they have no legal title—have standing to complain about searches of the houses in which they live. Chapman v. United States , 365 U. S. 610, 616–617 (1961), Bumper v. North Carolina , 391 U. S. 543, 548, n. 11 (1968).¶

Another point seems equally true: just because you have to entrust a third party with your data doesn’t necessarily mean you should lose all Fourth Amendment protections in it. Not infrequently one person comes into possession of someone else’s property without the owner’s consent. Think of the finder of lost goods or the policeman who impounds a car. The law recognizes that the goods and the car still belong to their true owners, for “where a person comes into lawful possession of the personal property of another, even though there is no formal agreement between the property’s owner and its possessor, the possessor will become a constructive bailee when justice so requires.” Christensen v. Hoover , 643 P. 2d 525, 529 (Colo. 1982) (en banc); Laidlaw, Principles of Bailment, 16 Cornell L. Q. 286 (1931). At least some of this Court’s decisions have already suggested that use of technology is functionally compelled by the demands of modern life, and in that way the fact that we store data with third parties may amount to a sort of involuntary bailment too. See ante, at 12–13 (majority opinion); Riley v. California , 573 U. S. ___, ___ (2014) (slip op., at 9).¶

Third , positive law may help provide detailed guidance on evolving technologies without resort to judicial intuition. State (or sometimes federal) law often creates rights in both tangible and intangible things. See Ruckelshaus v. Monsanto Co. , 467 U. S. 986, 1001 (1984). In the context of the Takings Clause we often ask whether those statecreated rights are sufficient to make something someone’s property for constitutional purposes. See id., at 10011003; Louisville Joint Stock Land Bank v. Radford , 295 U. S. 555, 590–595 (1935). A similar inquiry may be appropriate for the Fourth Amendment. Both the States and federal government are actively legislating in the area of third party data storage and the rights users enjoy. See, e.g., Stored Communications Act, 18 U. S. C. §2701 et seq. ; Tex. Prop. Code Ann. §111.004(12) (West 2017) (defining “[p]roperty” to include “property held in any digital or electronic medium”). State courts are busy expounding common law property principles in this area as well. E.g., Ajemian v. Yahoo!, Inc. , 478 Mass. 169, 170, 84 N. E. 3d 766, 768 (2017) (e-mail account is a “form of property often referred to as a ‘digital asset’ ”); Eysoldt v. ProScan Imaging , 194 Ohio App. 3d 630, 638, 2011–Ohio2359, 957 N. E. 2d 780, 786 (2011) (permitting action for conversion of web account as intangible property). If state legislators or state courts say that a digital record has the attributes that normally make something property, that may supply a sounder basis for judicial decisionmaking than judicial guesswork about societal expectations.¶

Fourth , while positive law may help establish a person’s Fourth Amendment interest there may be some circumstances where positive law cannot be used to defeat it.¶

Ex parte Jackson reflects that understanding. There this Court said that “[n]o law of Congress” could authorize letter carriers “to invade the secrecy of letters.” 96 U. S., at 733. So the post office couldn’t impose a regulation dictating that those mailing letters surrender all legal interests in them once they’re deposited in a mailbox. If that is right, Jackson suggests the existence of a constitutional floor below which Fourth Amendment rights may not descend. Legislatures cannot pass laws declaring your house or papers to be your property except to the extent the police wish to search them without cause. As the Court has previously explained, “we must ‘assur[e] preservation of that degree of privacy against government that existed when the Fourth Amendment was adopted.'' Jones , 565 U. S., at 406 (quoting Kyllo v. United States , 533 U. S. 27, 34 (2001)). Nor does this mean protecting only the specific rights known at the founding; it means protecting their modern analogues too. So, for example, while thermal imaging was unknown in 1791, this Court has recognized that using that technology to look inside a home constitutes a Fourth Amendment “search” of that “home” no less than a physical inspection might. Id., at 40.¶

Fifth , this constitutional floor may, in some instances, bar efforts to circumvent the Fourth Amendment’s protection through the use of subpoenas. No one thinks the government can evade Jackson ’s prohibition on opening sealed letters without a warrant simply by issuing a subpoena to a postmaster for “all letters sent by John Smith” or, worse, “all letters sent by John Smith concerning a particular transaction.” So the question courts will confront will be this: What other kinds of records are sufficiently similar to letters in the mail that the same rule should apply?¶

It may be that, as an original matter, a subpoena requiring the recipient to produce records wasn’t thought of as a¶

“search or seizure” by the government implicating the Fourth Amendment, see ante, at 2–12 (opinion of ALITO, J.), but instead as an act of compelled self-incrimination implicating the Fifth Amendment, see United States v. Hubbell , 530 U. S. 27, 49–55 (2000) (THOMAS, J., dissenting); Nagareda, Compulsion “To Be a Witness” and the Resurrection of Boyd, 74 N. Y. U. L. Rev. 1575, 1619, and n. 172 (1999). But the common law of searches and seizures does not appear to have confronted a case where private documents equivalent to a mailed letter were entrusted to a bailee and then subpoenaed. As a result, “[t]he common-law rule regarding subpoenas for documents held by third parties entrusted with information from the target is . . . unknown and perhaps unknowable.” Dripps, Perspectives on The Fourth Amendment Forty Years Later: Toward the Realization of an Inclusive Regulatory Model, 100 Minn. L. Rev. 1885, 1922 (2016). Given that (perhaps insoluble) uncertainty, I am content to adhere to Jackson and its implications for now.¶

To be sure, we must be wary of returning to the doctrine of Boyd v. United States , 116 U. S. 616. Boyd invoked the Fourth Amendment to restrict the use of subpoenas even for ordinary business records and, as JUSTICE ALITO notes, eventually proved unworkable. See ante, at 13 (dissenting opinion); 3 W. LaFave, J. Israel, N. King, & O. Kerr, Criminal Procedure §8.7(a), pp. 185–187 (4th ed. 2015). But if we were to overthrow Jackson too and deny Fourth Amendment protection to any subpoenaed materials, we would do well to reconsider the scope of the Fifth Amendment while we’re at it. Our precedents treat the right against self-incrimination as applicable only to testimony, not the production of incriminating evidence. See Fisher v. United States , 425 U. S. 391, 401 (1976). But there is substantial evidence that the privilege against selfincrimination was also originally understood to protect a person from being forced to turn over potentially incriminating evidence. Nagareda, supra, at 1605–1623; Rex v. Purnell , 96 Eng. Rep. 20 (K. B. 1748); Slobogin, Privacy at Risk 145 (2007).¶

*¶

What does all this mean for the case before us? To start, I cannot fault the Sixth Circuit for holding that Smith and Miller extinguish any Katz -based Fourth Amendment interest in third party cell-site data. That is the plain effect of their categorical holdings. Nor can I fault the Court today for its implicit but unmistakable conclusion that the rationale of Smith and Miller is wrong; indeed, I agree with that. The Sixth Circuit was powerless to say so, but this Court can and should. At the same time, I do not agree with the Court’s decision today to keep Smith and Miller on life support and supplement them with a new and multilayered inquiry that seems to be only Katz -squared. Returning there, I worry, promises more trouble than help. Instead, I would look to a more traditional Fourth Amendment approach. Even if Katz may still supply one way to prove a Fourth Amendment interest, it has never been the only way. Neglecting more traditional approaches may mean failing to vindicate the full protections of the Fourth Amendment.¶

Our case offers a cautionary example. It seems to me entirely possible a person’s cell-site data could qualify as his papers or effects under existing law. Yes, the telephone carrier holds the information. But 47 U. S. C. §222 designates a customer’s cell-site location information as “customer proprietary network information” (CPNI), §222(h)(1)(A), and gives customers certain rights to control use of and access to CPNI about themselves. The statute generally forbids a carrier to “use, disclose, or permit access to individually identifiable” CPNI without the customer’s consent, except as needed to provide the customer’s telecommunications services. §222(c)(1). It also requires the carrier to disclose CPNI “upon affirmative written request by the customer, to any person designated by the customer.” §222(c)(2). Congress even afforded customers a private cause of action for damages against carriers who violate the Act’s terms. §207. Plainly, customers have substantial legal interests in this information, including at least some right to include, exclude, and control its use. Those interests might even rise to the level of a property right.¶

The problem is that we do not know anything more. Before the district court and court of appeals, Mr. Carpenter pursued only a Katz “reasonable expectations” argument. He did not invoke the law of property or any analogies to the common law, either there or in his petition for certiorari. Even in his merits brief before this Court, Mr. Carpenter’s discussion of his positive law rights in cell-site data was cursory. He offered no analysis, for example, of what rights state law might provide him in addition to those supplied by §222. In these circumstances, I cannot help but conclude—reluctantly—that Mr. Carpenter forfeited perhaps his most promising line of argument.¶

Unfortunately, too, this case marks the second time this Term that individuals have forfeited Fourth Amendment arguments based on positive law by failing to preserve them. See Byrd , 584 U. S., at ___ (slip op., at 7). Litigants have had fair notice since at least United States v. Jones (2012) and Florida v. Jardines (2013) that arguments like these may vindicate Fourth Amendment interests even where Katz arguments do not. Yet the arguments have gone unmade, leaving courts to the usual Katz handwaving. These omissions do not serve the development of a sound or fully protective Fourth Amendment jurisprudence.¶