Carpenter, Your iPhone, and the Fourth Amendment


By: Peter Estall, Volume 102 Staff Member

A man robs a string of electronics stores. While investigating the robberies, the government arrests several suspects, one of whom confesses to the robberies.[1] The robber gives his cellphone number to the police; the FBI review his call records, and obtain a court order for information collected from 16 different phone numbers.[2] The information collected from these cellphones includes evidence providing the location of the defendant over 127 days.[3] The location evidence establishes that the defendant was near the scene of several robberies, and the defendant is convicted.[4] Have his Fourth Amendment rights protecting him against unreasonable search and seizure been violated?[5] These are the facts of United States v. Carpenter, a case currently before the Supreme Court. The general consensus is that the defendant’s constitutional rights were not violated[6]—and, in this case, the Sixth Circuit did not think so either.[7]

The Supreme Court will soon address the question itself.[8] Its decision could reverse nearly forty years of precedent.[9] The Supreme Court’s Fourth Amendment jurisprudence—which, since 1967, has primarily protected what the Court views to be “reasonable” expectations of privacy[10]—tends to strike a delicate balance between personal privacy and law enforcement interests.[11] The introduction of modern technology, including phones that can broadcast their users’ location[12] and phones that contain vast amounts of the users’ personal information, has upset this delicate balance.[13] The data collected by the location technology, known as cell-site location information (CSLI),[14] is collected and stored by cellphone service providers[15] and can be used to establish that a criminal defendant was near the scene of a crime when it was committed. CSLI is frequently used to obtain convictions.[16]

Generally, when information has been voluntarily disclosed to a third-party, the disclosing party no longer has a “legitimate expectation of privacy” with respect to the information,[17] and thus the Fourth Amendment no longer applies. This is the third-party doctrine.[18] The case most relevant to CSLI is Smith v. Maryland.[19] In Smith, the police installed a device capable of recording outgoing phone numbers from the defendant’s telephone without a warrant, but with the consent of the phone company.[20] The Supreme Court applied the third-party doctrine applied and held that the use of a pen register[21] did not violate any “legitimate” expectation of privacy, as the defendant had voluntarily disclosed the information recorded by the pen register to the telephone company.[22] Therefore, recording the numbers the defendant dialed was not a search and did not violate the Fourth Amendment.[23] The majority’s holding was effectively the state of third-party doctrine jurisprudence until the advent of smart phones upended Fourth Amendment jurisprudence.[24]

The Supreme Court has finally decided to tackle the question of how the third-party doctrine applies to information collected by smart phones in the digital era.[25] This question is not solely of constitutional nature. There are also statutory protections in place, notably the Stored Communications Act (SCA).[26] The most relevant provision of the SCA is § 2703, which requires that, to get a court order to obtain CSLI, the government must offer “specific and articulable facts” that show that there are “reasonable grounds” for believing “that the records . . . sought[] are relevant . . . to an ongoing criminal investigation.”[27] This standard, effectively “reasonable suspicion,”[28] is substantially lower than the probable cause requirement for the issuance of a warrant.[29]

In United States v. Carpenter, the Sixth Circuit upheld two armed robbery convictions.[30] Carpenter’s conviction rested in part on records obtained warrantlessly from his cell carrier showing that he was within a short distance of the robbery locations when the crimes occurred.[31] The defendants argued that the government had violated the Fourth Amendment’s warrant requirement by obtaining their CSLI for a substantial time period (for Carpenter, 127 days, and for his co-defendant, 88 days) without a warrant.[32] The defendants also argued that collecting CSLI was akin to warrantless GPS tracking, which the Supreme Court had recently held unlawful on trespass grounds.[33] The defendants equated long-term collection of CSLI with GPS tracking and argued that because a majority of the Supreme Court had recently expressed concerns about warrantless use of GPS tracking generally, the warrantless collection of CSLI was unconstitutional.[34] The Sixth Circuit rejected this argument, holding that the “government’s collection of business records containing [CSLI] was not a search under the Fourth Amendment.”[35] The stage is now set for a crucial Fourth Amendment battle at the highest court in the land.

The Supreme Court will once again, as in Riley v. California,[36] have to confront the challenge of maintaining its historical Fourth Amendment balance between personal privacy and law enforcement interests in the face of the advent of modern technology; here, instead of cellphones that contain immense amounts of personal information,[37] it is technology that broadcasts our location to third-parties. The Riley Court maintained the balance by requiring a warrant before police could search a suspect’s cellphone for evidence once arrested, thus establishing a simple bright-line rule for the police to follow. If the Court desires a bright line rule, it has few options. The Court may either effectively abrogate seventy years of the third-party doctrine, and hold that a warrant is required to obtain CSLI (unlikely, given the Court’s continual reaffirmation of the doctrine). The Court may also affirm the third-party doctrine in the digital era and condemn each and every person who has a cellphone to the risk that the government can and will obtain frightening amounts of their CSLI without a warrant,[38] which the Court may well view as indistinguishable from the data collected in Smith.[39]

There are other possibilities. The Court could, in the interests of maintaining the Fourth Amendment balance, decide that an individual does not “voluntarily convey” CSLI to their cell carrier.[40] Thus, the third-party doctrine, which has always required the voluntary disclosure of the incriminating information,[41] would not apply. The Fourth Amendment would apply instead. Or the Supreme Court could find that the Fourth Amendment requires “reasonable suspicion” to collect this data.[42] It could eliminate the third-party doctrine with respect to cellphones by holding the collection of CSLI by cell service providers to be involuntary. However, this may interfere too much with law enforcement interest for the Court to stomach. The “reasonable suspicion” approach currently required by 18 U.S.C. § 2703 appears to be working reasonably well,[43] but carries substantial privacy interest implications.[44]

The Court could also draw an arbitrary line in the collection of CSLI, establishing a point past which further CSLI collection requires a warrant. The point of this line would not necessarily be to be perfect, or to encompass all instances in which the Fourth Amendment would be (or may have been) violated, but to provide an extraordinarily bright line for law enforcement.[45] For instance, law enforcement could be permitted to obtain a week’s worth of CSLI without a warrant, but no more. This is a particularly simple rule that every single law enforcement officer would easily be able to follow.[46] The Court should not be afraid to draw such a line. Although arbitrary, the Court is no stranger to very fine distinctions drawn in an effort to provide clear guidance to law enforcement in Fourth Amendment cases.[47] Such a line can provide law enforcement the clear guidance they require, as well provide reasonable protection for the privacy interests of the general public.

Carpenter presents the Court with an opportunity to provide clarity to how courts should apply the third-party doctrine to CSLI, as well as provide guidance for other Fourth Amendment cases arising from modern technology. There is no doubt that this question is extraordinarily difficult to answer. If the Court affirms the third-party doctrine, the privacy interests of the general public will still be subject to substantial governmental intrusion. On the other hand, if the Court disavows the third-party doctrine, law enforcement will suffer a substantial limitation on its ability to detect and prosecute criminals.[48] If the Court attempts to take a middle road, the rule it develops will be, by necessity, over- or underinclusive, and there will be cases on the margins where defendants feel justifiably aggrieved by the arbitrariness of the rule the Court will have laid down. Ultimately, however, it is the Court’s function to “say what the law is.”[49] The Court must speak on the substance of the law regarding CSLI. If the price of a clear rule is some arbitrariness and close cases, that is the price that must be paid.

  1. United States v. Carpenter, 819 F.3d 880, 884 (6th Cir. 2016), cert. granted, 137 S. Ct. 2211 (2017) (No. 16-402).
  2. Id.
  3. Id. at 886.
  4. Id.
  5. U.S. Const. amend. IV.
  6. E.g., United States v. Graham, 824 F.3d 421, 424 (4th Cir. 2016) (en banc).
  7. Carpenter, 819 F.3d at 883.
  8. 137 S. Ct. 2211 (2017) (granting certiorari in Carpenter, 819 F.3d 880).
  9. The canonically relevant case is Smith v. Maryland, 442 U.S. 735 (1979).
  10. Katz v. United States, 389 U.S. 347, 361 (1967) (Harlan, J., concurring).
  11. Illinois v. McArthur, 531 U.S. 326, 331 (2001) (“[W]e balance the privacy-related and law enforcement-related concerns.”) (citing Delaware v. Prouse, 440 U.S. 648, 654 (1979) and United States v. Brignoni-Ponce, 422 U.S. 873, 878 (1975)).
  12. Peter Maass and Megha Rajagopalan, That’s No Phone. That’s My Tracker., N.Y. Times (July 13, 2012), To see the (rather frightening) extent of the information your cellphone or carrier may have collected regarding your movements, visit to view your Google “Timeline” (click on “Menu” in the upper left-hand corner, then “Your timeline” on the menu that appears). This information is collected via GPS; it is not CSLI, but the extent of the information collected is illustrative nonetheless.
  13. See Riley v. California, 134 S. Ct. 2473, 2484 (2014) (recognizing that the advent of modern cellphones has introduced serious complications to historical Fourth Amendment jurisprudence); Id. at 2496–97 (Alito, J. concurring in part and dissenting in part) (“[W]e should not mechanically apply the rule used in the pre-digital era to the search of a cellphone.”).
  14. United States v. Graham, 824 F.3d 421, 424 (4th Cir. 2016) (en banc). For an excellent overview of the capabilities and technology of CSLI, see Steven M. Harkins, Note, CSLI Disclosure: Why Probable Cause is Necessary to Protect What’s Left of the Fourth Amendment, 68 Wash. & Lee L. Rev. 1875, 1881–85 (2011).
  15. Id. at 425.
  16. E.g., Graham, 824 F.3d at 424 (allowing the use of CSLI to place a defendant near the scene of the crime at the time the crime occurred).
  17. Id. at 742.
  18. See Orin S. Kerr, The Case for the Third-Party Doctrine, 107 Mich. L. Rev. 561, 561.
  19. 442 U.S. 735 (1979); see Joshua Vittor, Note, What Would a Martian Think of Cellphones? The Third-Party Doctrine and Technological Extensions of the Human Self, 10 Harv. L. & Pol’y Rev. 255, 261–64 (2016) (cataloging arguments against Smith v. Maryland, 442 U.S. 735 (1979)).
  20. Smith, 442 U.S. at 736–37. The defendant was later convicted based on the evidence obtained from the device. Id. at 738–39.
  21. See id. at 736, n.1 (“A pen register is a mechanical device that records the numbers dialed on a telephone by monitoring the electrical impulses caused when the dial on the telephone is released. It does not overhear oral communications and does not indicate whether calls are actually completed.”) (internal citations omitted). Courts have analogized the data the pen register collected in Smith to CSLI collected by cell carriers today. E.g., Graham, 824 F.3d at 427 (“The CSLI [collected] was necessary to route Defendants’ [communications, just like] the dialed numbers recorded by the pen register in Smith.”).
  22. Smith, 442 U.S. at 745–46.
  23. Id.
  24. See Riley v. California, 134 S. Ct. 2473, 2484 (2014) (recognizing that the advent of modern technology has seriously altered society, and consequently, law). In Riley, the Court confronted warrantless police searches of defendants’ cellphones. Id. Having resolved that issue by requiring a warrant prior to searching a cellphone, Id. at 2495, the Court still must confront the issue of using third-party created and maintained CSLI. Unless it ducks the question, the Court will do so in Carpenter v. United States. 819 F.3d 880 (6th Cir. 2016), cert. granted, 137 S. Ct. 2211 (2017) (No. 16-402).
  25. Lawrence Hurley, U.S. Supreme Court to Settle Major Cellphone Privacy Case, Reuters (June 15, 2017), (
  26. Pub. L. No. 99–508, § 201[a], 100 Stat. 1860 (1986) (codified at 18 U.S.C. §§ 2701–11).
  27. 18 U.S.C. § 2703(d) (2012). However, if the cellphone service provider consents to the government’s request for the data, no court order is needed. § 2703(c)(C).
  28. In re United States for an Order Pursuant to 18 U.S.C. §2703(d), 707 F.3d 283, 287 (4th Cir. 2013).
  29. U.S. Const., amend IV.
  30. United States v. Carpenter 819 F.3d 880, 883 (6th Cir. 2016), cert. granted, 137 S. Ct. 2211 (2017) (No. 16-402).
  31. Id.
  32. Id.
  33. United States v. Jones, 565 U.S. 400, 410–13 (2012). While the government in Jones had a warrant for placing a GPS tracker on the defendant’s vehicle, the government conceded it had failed to comply with the warrant. Id. at 402 n.1. A majority of the justices expressed concerns about long-term GPS monitoring, though this was addressed in separate concurrences. See id. at 424 (Alito, J., concurring) (“[T]he Court’s reasoning largely disregards what is really important (the use of a GPS for the purpose of long-term tracking).”); id. at 416 (Sotomayor, J., concurring) (“I agree with Justice Alito that, at the very least, longer term GPS monitoring in investigations of most offenses impinges on expectations of privacy.” (internal quotations omitted)). Justice Sotomayor also called for a reexamination of the third-party doctrine in the digital era. Id. at 417 (“[I]t may be necessary to reconsider the premise that an individual has no reasonable expectation of privacy in information voluntarily disclosed to third parties.”).
  34. Carpenter, 819 F.3d at 888.
  35. Id. at 890.
  36. 134 S. Ct. 2473 (2014).
  37. See id. at 2484 (2014).
  38. It is important to note, however, that while the government does not need probable cause to obtain CSLI, as noted above, there are some statutory protections in place. E.g., 18 U.S.C. § 2703(d) (2017) (the government may obtain a court order for CSLI “if the governmental entity offers specific and articulable facts showing that there are reasonable grounds to believe that the contents of a wire or electronic communication, or the records or other information sought, are relevant and material to an ongoing criminal investigation”). However, the government may simply ask the provider for the CSLI, and the provider may consent. 18 U.S.C. § 2703(c)(1)(C) (2017).
  39. Courts have consistently held that routing information (e.g., mail addresses, IP addresses, etc.) is voluntarily conveyed to the third party who needs the information to complete the requested task (e.g., delivering a letter, visting a webpage, etc.), and thus that the third-party doctrine applies. See, e.g., United States v. Forrester, 512 F.3d 500, 511 (9th Cir. 2008) (“The contents [of a communication] may deserve Fourth Amendment protection, but the address . . . do[es] not”).
  40. This would effectively vindicate Judge Wynn’s dissent in United States v. Graham, 824 F.3d 421, 441–50 (4th Cir. 2016). (Wynn, J., dissenting). Judge Wynn’s argument was similar to Justice Marshall’s position in Smith. See Smith v. Maryland, 442 U.S. 735, 748–52 (1979) (Marshall, J., dissenting), superseded by statute, Electronic Communications Privacy Act of 1986, Pub. L. No. 99–508, 100 Stat. 1848, as recognized in In re Certified Question of Law, 858 F.3d 591 (FISA Ct. Rev. 2016).
  41. Smith, 442 U.S. at 743–44.
  42. See Illinois v. Wardlow, 528 U.S. 119 (2000). This would accord with § 2703(d), which requires “specific and articulable facts showing that there are reasonable grounds [that the individual is engaged in criminal activity]” before obtaining a court order for CSLI. This standard is similar to that developed for police stops (which are seizures, but not arrests) of citizens suspected of criminal behavior in Terry. See Terry v. Ohio, 392 U.S. 1, 21 (1968) (“And in justifying the particular intrusion the police officer must be able to point to specific and articulable facts which, taken together with rational inferences from those facts, reasonably warrant that intrusion.”). Terry accepted that there were different levels of seizures (a seizure is not binary), which might accord with the notion advanced by Justice Marshall in Smith that privacy is not a binary value. See Smith, 442 U.S. at 749 (Marshall, J., dissenting). Perhaps collecting CSLI which is less precise than GPS data is less invasive, and therefore should have a lower standard. See Alabama v. White, 496 U.S. 325, 328–29 (1990) (“These factors [for determining probable cause needed to obtain a warrant] are also relevant in the reasonable-suspicion context, although allowance must be made in applying them for the lesser showing required to meet th[e lower] standard [of reasonable suspicion].”).
  43. See, e.g., Graham, 824 F.3d 421; United States v. Carpenter 819 F.3d 880, 883 (6th Cir. 2016).
  44. Arguably, this is why the Supreme Court agreed to hear Carpenter; to resolve the conflict between privacy and law enforcement interests in CSLI cases.
  45. This would accord with the general preference of the Supreme Court for providing bright lines to law enforcement in areas covered by the Fourth Amendment. See Riley v. California, 134 S. Ct. 2473, 2491 (2014) (“[This Court has a] general preference [for] provid[ing] clear guidance to law enforcement through categorical rules.”).
  46. The strongest proponents of the third-party doctrine justify it on the grounds that it provides the ex ante clarity to government actors necessary to justify exclusion of evidence in criminal proceedings. See, e.g., Kerr, supra note 16 at 581–86. Professor Kerr also maintains that the third-party doctrine is the most effective means to provide this clarity. Id. at 581. I do not disagree with Professor Kerr in the slightest that such an extreme sanction as exclusion requires clear guidance to police. I am concerned that the third-party doctrine does not adequately protect privacy interests, particularly in an age where our cellphones broadcast our locations. Therefore, I am in favor of a clear, constitutional rule that does not permit the government to access the massive amount of CSLI produced by my cellphone with the ease that it currently does. I am less concerned about the potential over-inclusiveness or under-inclusiveness of a particular arbitrary rule; almost all bright-line rules will necessarily involve some cases on the margin in which parties feel justifiably aggrieved by operation of the rule.
  47. E.g., Georgia v. Randolph, 547 U.S. 103, 121–22 (accepting that an (admittedly arbitrary) line drawn in the sand was necessary to provide clear rules to police and worth the arbitrariness).
  48. Of course, every time the Court extends Fourth Amendment rights, law enforcement suffers a corresponding blow.
  49. Marbury v. Madison 5 U.S. (1 Cranch) 137, 177 (1803).
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