The Supreme Court’s decision in Katz v United States made people’s reasonable expectations of privacy the touchstone for determining whether state surveillance amounts to a search under the Fourth Amendment. Ever since Katz, Supreme Court justices and numerous scholars have referenced the inherent circularity of taking the expectations-of-privacy framework literally: people’s expectations of privacy depend on Fourth Amendment law, so it is circular to have the scope of the Fourth Amendment depend on those same expectations. Nearly every scholar who has written about the issue has assumed that the circularity of expectations is a meaningful impediment to having the scope of the Fourth Amendment depend on what ordinary people actually expect. But no scholar has tested the circularity narrative’s essential premise: that popular sentiment falls into line when salient, well-publicized changes in Fourth Amendment law occur.

Our Article conducts precisely such a test. We conducted surveys on census-weighted samples of US citizens immediately before, immediately after, and long after the Supreme Court’s landmark decision in Riley v California. The decision in Riley was unanimous and surprising. It substantially altered Fourth Amendment law on the issue of the privacy of people’s cell phone content, and it was a major news story that generated relatively high levels of public awareness in the days after it was decided. We find that the public began to expect greater privacy in the contents of their cell phones immediately after the Riley decision, but this effect was small and confined to the 40 percent of our sample that reported having heard of the decision. One year after Riley, these heightened expectations had disappeared completely. There was no difference from baseline two years after Riley either, with privacy expectations remaining as they were prior to the decision. Our findings suggest that popular privacy expectations are far more stable than most judges and commentators have been assuming. Even in the ideal circumstance of a clear, unanimous, and widely reported decision, circularity in Fourth Amendment attitudes is both weak and short lived. In the longer term, Fourth Amendment circularity appears to be a myth.


It is very difficult to find any proposition in Fourth Amendment law to which every judge, lawyer, and scholar subscribes. One striking point about which nearly everyone—left, right, and center—agrees, however, is that there is a degree of circularity in the Katz v United States1 “reasonable expectations of privacy” test.2 Among those expressing concern about this circularity are Justices Samuel Alito, Anthony Kennedy, Antonin Scalia, and John Paul Stevens, Judges Alex Kozinski, Richard Posner, and George MacKinnon, and Professors Jed Rubenfeld, Dan Solove, Amitai Etzioni, Erwin Chemerinsky, David Sklansky, and Paul Schwartz.3 In this Article, we show that this widely shared concern is misplaced.

Justice John Marshall Harlan II’s opinion in Katz makes a person’s reasonable expectations of privacy the touchstone for determining whether police surveillance amounts to a search and, therefore, is subject to restrictions under the Fourth Amendment.4 Under Katz and the numerous cases that follow its approach, the government conducts a search when it invades an “expectation of privacy . . . that society is prepared to recognize as ‘reasonable.’”5 If the government’s surveillance intrudes on such an expectation, the Fourth Amendment is implicated and the government must either get a search warrant or satisfy one of the limited exceptions to the warrant requirement.6 If the government’s surveillance does not implicate a reasonable expectation of privacy, then the Fourth Amendment is inapplicable and no warrant is required.7

The exact meaning of Katz’s reasonable-expectation-of-privacy test is controversial, but its text has led some scholars to argue that the test should depend in part on how everyday members of the public think about privacy.8 And in some prominent post-Katz cases, the Supreme Court has said it is doing exactly that.9 The problem that many have identified with this approach to Katz is that reasonable people should expect the privacy rights granted to them by the courts. So expectations define the scope of legal protection, but the legal protections themselves should define the expectations.

This potential circularity gives rise to a practical problem. Once the state begins using an investigative technique, and especially once the courts authorize the state to do so, ordinary people’s expectations of privacy may adjust. Thus, even if people expected privacy in a context at some earlier point in time, subsequent actions by the government can erode these expectations, enabling the state to conduct invasive surveillance in the future without having to secure a warrant. If this understanding of expectations is correct, the Fourth Amendment provides little protection against a government that acts strategically; all it need do is move incrementally and publicize what it is doing. Further, the judicial determination of whether an expectation of privacy exists would be largely empty; even if the court gets the answer “wrong,” public expectations would soon adapt to make it “right.” For those who argue that the reasonableness of a privacy expectation should depend on whether the expectation is widely shared, this is an especially salient problem. If public expectations are a function of whatever the Supreme Court said last, then the Court accounting for such expectations would result in it talking to itself.

The Fourth Amendment circularity hypothesis is intuitive and easy to grasp. There are just two problems with the circularity story: (1) there is no hard empirical evidence supporting it, and (2) an empirical literature in political science provides ample reason to doubt it. In this Article, we present new data that suggest that popular expectations of privacy are very stubborn. Though expectations move a little right after a major Supreme Court decision substantially changes Fourth Amendment law, within a span of months expectations snap right back to where they were beforehand and they remain stable thereafter. As best we can tell from this data, the circularity of reasonable expectations of privacy is a myth.

Part I of the Article presents the problem of circularity. At stake in this discussion is the feasibility of incorporating public expectations into the doctrine. If expectations are independent of current case law, then looking to public expectations can provide a correcting impulse against an out-of-touch judiciary. If, on the other hand, expectations merely reflect what courts have said, then there is no point to considering public attitudes; no information would be gained. The Part begins by explaining the Supreme Court’s concern that expectations of privacy would become an empty concept, and that a government could strategically condition the populace to accept ever-greater privacy invasions. We then identify many Fourth Amendment scholars expressing the same concern. Lastly, we examine a literature from political science and psychology commenting on public reactions to Supreme Court decisions. This literature informed our skepticism that the public would uncritically mirror the Court’s rulings.

In Part II, we describe the case at the core of our study: Riley v California.10 The case established a new rule for the searching of electronic devices incident to arrest. This case was well suited to prompting a major change in public expectations. The ruling was clear; it was broad; it was surprising; it was unanimous; and it prompted a torrent of media coverage. As Fourth Amendment cases go, we could not have hoped for better; it stacked the deck in favor of finding a change of expectation. And yet no lasting change was observed.

In Part III, we present the empirical study itself. We recruited census-representative participants in four waves: one right before the decision, one right after, a one-year follow-up, and a two-year follow-up. We found a small shift in the direction of the Court’s decision in the survey conducted immediately after the decision came down. However, this shift (1) was specific to the exact question in Riley and did not generalize to related questions, (2) was present only among those who reported having heard of the decision, and (3) disappeared the following year. Put another way, the Supreme Court managed to move privacy expectations only slightly and only for a very short time. Based on these data, circularity does not seem to be a problem.

In Part IV, we examine the implications of these data for Fourth Amendment doctrine and relate our findings back to the political science literature on the effects of Supreme Court decisions on public attitudes. We also show that a nearly simultaneous Supreme Court decision, Burwell v Hobby Lobby Stores, Inc,11 had a short-lived, polarizing effect on the public. This finding underscores the complicated interplay between the Supreme Court and the general public and adds further reason to believe that circularity is neither strong nor common.

  • 1. 389 US 347 (1967).
  • 2. Id at 362 (Harlan concurring).
  • 3. See text accompanying notes 5-36.
  • 4. Katz, 389 US at 361 (Harlan concurring) (stating that police conduct amounts to a search, thereby implicating the Fourth Amendment, when “a person [exhibits] an actual (subjective) expectation of privacy and [when] the expectation [is] one that society is prepared to recognize as ‘reasonable’”). The test from Harlan’s concurrence subsequently became the key Fourth Amendment inquiry, embraced repeatedly by the Supreme Court over time. See, for example, California v Ciraolo, 476 US 207, 211 (1986) (“The touchstone of Fourth Amendment analysis is whether a person has a ‘constitutionally protected reasonable expectation of privacy.’”), citing Katz, 389 US at 360 (Harlan concurring); Kyllo v United States, 533 US 27, 32–33 (2001) (describing the Supreme Court majority’s application of Harlan’s Katz test in several cases).
  • 5. Katz, 389 US at 361 (Harlan concurring).
  • 6. See Riley v California, 134 S Ct 2473, 2482 (2014).
  • 7. See Florida v Riley, 488 US 445, 449 (1989).
  • 8. See, for example, Christopher Slobogin, Privacy at Risk: The New Government Surveillance and the Fourth Amendment 114 (Chicago 2007); Jeremy A. Blumenthal, Meera Adya, and Jacqueline Mogle, The Multiple Dimensions of Privacy: Testing Lay “Expectations of Privacy,” 11 U Pa J Const L 331, 336–37 (2009); Henry F. Fradella, et al, Quantifying Katz: Empirically Measuring “Reasonable Expectations of Privacy” in the Fourth Amendment Context, 38 Am J Crim L 289, 338–42 (2011); Matthew B. Kugler and Lior Jacob Strahilevitz, Actual Expectations of Privacy, Fourth Amendment Doctrine, and the Mosaic Theory, 2015 S Ct Rev 205, 219, 230; Christine S. Scott-Hayward, Henry F. Fradella, and Ryan G. Fischer, Does Privacy Require Secrecy? Societal Expectations of Privacy in the Digital Age, 43 Am J Crim L 19, 45–58 (2015); Christopher Slobogin and Joseph E. 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 (1993); Bernard Chao, et al, Why Courts Fail to Protect Privacy: Race, Age, Bias, and Technology, 106 Cal L Rev *6–19 (forthcoming 2018), archived at‌MA8V‌-PJKT.
  • 9. See text accompanying note 27.
  • 10. 134 S Ct 2473 (2014).
  • 11. 134 S Ct 2751 (2014).