by Lucy Sundelson*

The Supreme Court has long held that under the Fourth Amendment to the Constitution, “warrantless searches are per se unreasonable,” except in a few limited circumstances.1 One exception to the rule is the automobile exception, which allows police to conduct a warrantless search of a vehicle and its contents with probable cause. Over time, the automobile exception has expanded beyond its original purpose, allowing police to search cars and their contents indiscriminately, and its modern application threatens to swallow the warrant requirement altogether. Computer technology offers an opportunity for courts to limit the breadth of the automobile exception and ensure it remains faithful to the purpose of the Fourth Amendment: given the profoundly private information computers and cell phones store, courts must hold that the exception does not extend to such devices. While the Court has not ruled directly on this issue, two recent decisions dealing with other exceptions to the warrant requirement make clear that the Justices agree electronic data must be handled differently than other belongings in the Fourth Amendment context. Courts should use these decisions to prohibit the warrantless search of cell phones and other similar electronic devices, even when they are found within cars.

The automobile exception to the warrant requirement of the Fourth Amendment, which allows police to conduct a warrantless search of a vehicle if there is probable cause, has long been the subject of criticism.2 In particular, legal scholars have pointed to the broadened application of the exception beyond its original purpose to allow police to search cars that could be easily transported out of their jurisdiction. Today, the exception is used to justify searches of nearly all the contents found in a car, including personal effects that were once off limits, such as purses, wallets, and private files. The result of this expansion is that the exception has “all but swallowed the rule.”3

In the digital age, a new question has emerged about the breadth of the automobile exception: does it allow warrantless searches of computers and smartphones found in cars? Absent clear direction on this issue from the Supreme Court, a circuit split has emerged. This Contribution argues that the Fourth Amendment prohibits warrantless searches of electronic devices, such as cell phones, that are capable of storing “vast quantities of personal data.”4 Moreover, this constitutional protection applies even when such devices are found in vehicles; the automobile exception cannot justify the warrantless search of computers capable of storing profoundly private information. By limiting the exception as it applies to electronic data, courts would be more faithful to the “basic principles” of the Fourth Amendment.5

The Fourth Amendment protects all Americans against “unreasonable searches and seizures.”6 The Supreme Court has held that a search is “reasonable” only in cases where police have obtained a warrant.7 The warrant requirement thus adds a layer of judicial protection for individual privacy: police must obtain permission from an impartial judge before invading private spaces.8 This judicial review is an essential mechanism for the protection of American liberty: the Fourth Amendment ensures our private lives are shielded against arbitrary searches and unfettered control by the government.

Because of its fundamental importance, the warrant requirement is “subject only to a few specifically established and well-delineated exceptions.”9 Many of those exceptions are based in the same justification, that it is not practical to require that police obtain a warrant under certain emergency circumstances.10 The exigent circumstances exception, for example, allows police officers to conduct a search when they reasonably believe such a search “was necessary to prevent physical harm to the officers or other persons.”11 Similarly, the search incident to arrest exception allows a warrantless search to disarm a potentially dangerous arrestee and to prevent the destruction of evidence within the arrestee’s reach.12

As originally conceived, the automobile exception is similarly grounded in concerns about emergency circumstances: the exception allows a warrantless search “where it is not practicable to secure a warrant, because the vehicle can be quickly moved out of the locality or jurisdiction in which the warrant must be sought.”13 This “ready mobility” justification serves to limit the breadth of the exception: a search without a warrant is only justified if there was legitimate concern that evidence could be quickly transported away from police’s reach.

Since the exception was created, however, courts have added an additional justification that has broadened its application dramatically: the “lesser expectation of privacy” within cars compared to other, more private spaces, such as homes.14 Over time, the ready mobility justification has “slowly given way to the ‘lesser expectation of privacy’ rationale.”15 Under the modern automobile exception, police can conduct warrantless searches of vehicles that have already been seized or are incapable of being moved.16

The lesser expectation of privacy rationale has allowed the exception to expand far beyond its original purpose. Today, police can conduct warrantless searches of closed containers within vehicles, even if those containers could be safely seized and held while a warrant is obtained.17 Thus, the exception now justifies searches of items that would be off limits if they were found outside of a car, including private, sealed containers. As a result of this expansion, “[p]olice searches by warrant are the rare exception and not the norm.”18 Surely, the Fourth Amendment does not tolerate such a reality.

The modern reach of the automobile exception has also served as a tool to over-police people of color by allowing more intrusive searches during traffic stops. Researchers have already established that police use of traffic stops is “skewed along racial lines.”19 Given the modern iteration of the automobile exception, police can conduct warrantless searches of everything inside someone’s car during a traffic stop. The result is that “no form of direct government control comes close to these [traffic] stops in sheer numbers, frequency, proportion of the population affected, and in many instances, the degree of coercive intrusion.”20 The expansion of the exception therefore poses a serious danger to the privacy protections afforded by the Fourth Amendment, particularly for people of color. In order to remain faithful to the original purpose of the warrant requirement, courts must limit the application of the automobile exception more strictly.

Electronic data offers one particularly important opportunity for courts to limit the reach of the exception. Computers and cell phones implicate much more profound privacy interests than many other containers stored in cars because of the type and volume of data they store. “The sum of an individual’s private life can be reconstructed” via a search of a personal computer or cell phone, which can hold thousands of personal photographs and messages, medical and financial information, and data about a person’s travel and activities.21 Moreover, such devices are often found in cars: Americans carry their cell phones with them everywhere, and modern vehicle computers record various types of personal data, such as location and route histories, videos, as well as smart phone data.22 In order to fortify the protections of the Fourth Amendment, courts must treat such devices differently than the containers covered under the automobile exception.23

Despite the clear differences between computer data and other personal information, lower courts have struggled to come to a consensus about how the automobile exception should be applied to electronic devices, and a circuit split has developed. However, two recent decisions by the Court suggest that the Justices are hesitant to allow warrantless searches of electronic data. Together, the decisions offer a path to limiting the continued expansion of the automobile exception and reenforcing the strength of the Fourth Amendment as it applies in our modern technological world.

In Riley v. California, the Court held that a warrant is required for the search of a cell phone seized incident to arrest.24 In his majority opinion, Chief Justice Roberts explained that “[m]odern cell phones, as a category, implicate privacy concerns far beyond those implicated by the search of a cigarette pack, a wallet, or a purse.”25

Riley addresses searches of cell phones in the context of the search incident to arrest exception, not the automobile exception. Moreover, the Riley Court noted that while “the search incident to arrest exception does not apply to cell phones, other case-specific exceptions may still justify a warrantless search of a particular phone.”26 Some lower courts have interpreted this to mean that the automobile exception justifies the warrantless search of electronic devices found in cars.27 This interpretation ignores the Court’s careful analysis of the application of the warrant requirement to the search of electronic devices by allowing police to search private electronic information indiscriminately as long as it is found within a vehicle.28 It also ignores that the “case-specific exceptions” noted in Riley involve only exigent circumstances;29 the decision makes no suggestion that the privacy interests implicated by electronic devices are reduced in the automobile context. Lower court decisions that treat electronic devices found in cars the same as other automobile containers thus “both undervalue . . . core Fourth Amendment protection” of personal information “and ‘untether’ the exception ‘from the justifications underlying it.’”30

Other lower courts have followed an interpretation that is more faithful to the purpose of the Fourth Amendment. These decisions “extend the reasoning in Riley from the search incident to arrest exception to the vehicle exception.”31 In United States v. Camou, for example, the Ninth Circuit explains, “[j]ust as ‘[c]ell phones differ in both a quantitative and a qualitative sense from other objects that might be kept on an arrestee’s person,’ so too do cell phones differ from any other object officers might find in a vehicle.”32 In Camou, the court explained that the rule in Riley should apply to the automobile exception context because “the permissible scope of a vehicle exception search is ‘broader’ than that of a search incident to arrest.”33 In other words, since the automobile exception allows warrantless searches of the entire contents of a vehicle, it permits potentially greater intrusion than a search incident to arrest. Under the Camou rule, such an intrusion must be strictly controlled.

In Carpenter v. United States, the Court offered additional indication that exceptions to the warrant requirement must be limited in the context of electronic data.34 Here, the Court held that the third-party doctrine—another exception to the warrant requirement that stands for the idea that “a person has no legitimate expectation of privacy in information [they] voluntarily turn[] over to third parties”—did not allow the warrantless search of an individual’s cell-site location information.35 The Court explained that the heightened privacy interests identified in Riley apply broadly to searches of electronic data, not just searches of cell phones incident to arrest.

Given that the Supreme Court has now repeatedly held that a search of computer data requires a warrant, it would be incongruous to hold that the automobile exception allows the warrantless search of such data.36 A faithful reading of the requirements of the Fourth Amendment—as well as the original purpose of the automobile exception—would prohibit the warrantless search of electronic devices absent exigent circumstances. Such a rule should cover computers and modern cell phones, which have the capacity to store gigabytes of “many distinct types of information.”37 The rule should also apply to other electronic devices found in cars, such as vehicle computers, that have a similar storage capacity or can be connected to smart phones. Consistent application of this rule would fortify the original purpose of the Fourth Amendment—to protect private information from indiscriminate search and control by law enforcement—in the modern world. The rule would also mark an important step to limiting the overreach of the automobile exception and preventing the exception from swallowing the original rule.

* Lucy Sundelson is a J.D. Candidate (2024) at New York University School of Law. This Contribution is a commentary on the problem at the 2023 William B. Spong, Jr. Moot Court Tournament, hosted by William & Mary Law School. The question presented was whether the Supreme Court’s holding in Riley v. California, 573 U.S. 373 (2014)—that police must obtain a warrant to search cell phone data seized incident to arrest—requires that police obtain a warrant in order to search private electronic data stored on a vehicle computer. This Contribution distills one side of the argument, and the views expressed herein do not necessarily represent the author’s views.

1. Katz v. United States, 389 U.S. 347, 357 (1964).

2. See, e.g., Martin L. O’Connor, Vehicle Searches—The Automobile Exception: The Constitutional Ride from Carroll v. United States to Wyoming v. Houghton, 16 Touro L. Rev. 393, 433–34 (2000) (critiquing the Supreme Court’s liberal application of the automobile exception).

3. Id. at 427 (quoting Florida v. White, 526 U.S. 559, 569 (1996) (Stevens, J., dissenting)).

4. Riley v. California, 573 U.S. 373, 386 (2014).

5. Katz, 389 U.S. at 357.

6. U.S. Const. amend. IV.

7. Riley, 573 U.S. at 382 (“Such a warrant ensures that the inferences to support a search are ‘drawn by a neutral and detached magistrate instead of being judged by the officer engaged in the often competitive enterprise of ferreting out crime.’”) (quoting Johnson v. United States, 333 U.S. 10, 14 (1948)).

8. See Katz, 389 U.S. at 357 (“Searches conducted outside the judicial process . . . are per se unreasonable under the Fourth Amendment.”).

9. Id.

10. See Muhammad Mustafa, The Post-Carpenter Automobile Exception, 101 B.U. L. Rev. 399, 404–05 (2021) (“Such exceptions include, but are not limited to, the exigent circumstances exception, Terry stops, and searches incident to arrest.”).

11. United States v. McConney, 728 F.2d 1195, 1199 (9th Cir. 1984) (en banc), overruled on other grounds by Estate of Merchant v. Comm’r, 947 F.2d 1390, 1392–93 (9th Cir. 1991).

12. See Chimel v. California, 395 U.S. 752, 764 (1969) (asserting this proposition).

13. Carroll v. United States, 267 U.S. 132, 153 (1925).

14. California v. Carney, 471 U.S. 386, 391 (1985) (“Even in cases where an automobile was not immediately mobile, the lesser expectation of privacy resulting from its use as a readily mobile vehicle justified application of the vehicular exception.”).

15. Mustafa, supra note 10, at 407.

16. See United States v. Johns, 469 U.S. 478, 487–88 (1985) (holding that evidence found during warrantless search of two trucks that had already been seized by police was admissible).

17. See, e.g., Wyoming v. Houghton, 526 U.S. 295 (1999) (holding that the search of vehicle passenger’s purse was allowed under the automobile exception); California v. Acevedo, 500 U.S. 565, 580 (1991) (affirming that the warrantless search of a bag containing marijuana in a car was justified under the automobile exception).

18. O’Connor, supra note 2, at 434.

19. Sarah A. Seo, Policing the Open Road: How Cars Transformed American Freedom 6 (2019); see also Anthony J. Ghiotto, Traffic Stop Federalism: Protecting North Carolina Black Drivers from the United States Supreme Court, 48 U. Balt. L. Rev. 323, 323 (2019) (“Black drivers face a different constitutional reality than whites the moment they step behind the wheel in North Carolina. Although black drivers represent only about twenty-two percent of the North Carolina population, thirty-two percent of all traffic stops involve black drivers.”).

20. Seo, supra note 19, at 6; see also David A. Harris, Driving While Black and All Other Traffic Offenses: The Supreme Court and Pretextual Traffic Stops, 87 J. Crim. L. & Criminology 544, 560 (1997) (“[P]olice use traffic regulations to investigate many innocent citizens . . . and African-Americans and Hispanics are the targets of choice for law enforcement.”).

21. Riley, 573 U.S. at 394.

22. See Patrick Howell O’Neill, Meet Berla, the Little-Known Company That Can Pull Smartphone Data from Your Car, CyberScoop (September 11, 2017), (“Phones plugged into cars often carelessly give away data including SMS messages, contact lists, emails, social media feeds and more.”).

23. See Riley, 573 U.S. at 393 (“The United States asserts that a search of all data stored on a cell phone is ‘materially indistinguishable’ from searches of . . . physical items. . . . That is like saying a ride on horseback is materially indistinguishable from a flight to the moon.”).

24. 573 U.S. 373.

25. Id. at 393.

26. Id. at 401–02.

27. See, e.g., United States v. Figueroa, No. 12-cr-00233, 2014 U.S. Dist. LEXIS 146722, at 17 (S.D.N.Y. Oct. 1, 2014) (holding that Riley “is limited to a search of a cell phone incident to arrest”).

28. See Riley, 573 U.S. at 393 (“A conclusion that inspecting the contents of an arrestee’s pockets works no substantial additional intrusion on privacy beyond the arrest itself may make sense as applied to physical items, but any extension of that reasoning to digital data has to rest on its own bottom.”).

29. Id. at 388 (noting that a warrant is not required if delay “would gravely endanger . . . lives”) (quoting Warden, Md. Penitentiary v. Hayden, 387 U.S. 294, 298–299 (1967)).

30. Collins v. Virginia, 138 S. Ct. 1663, 1667 (2018) (quoting Riley, 573 U.S. at 386).

31. United States v. Camou, 773 F.3d 932, 942 (9th Cir. 2014).

32. Id. at 942–43.

33. Id. at 941 (“If there is probable cause to believe a vehicle contains evidence of criminal activity, [Ross] authorizes a search of any area of the vehicle in which the evidence might be found.”).

34. 138 S. Ct. 2206, 2223 (2018) (“Here the progress of science has afforded law enforcement a powerful new tool to carry out its important responsibilities. At the same time, this tool risks Government encroachment of the sort the Framers . . . drafted the Fourth Amendment to prevent.”).

35. Id. at 2216 (quoting Smith v. Maryland, 442 U.S. 735, 743–44 (1979)).

36. See Mustafa, supra note 10, at 429 (“The logic and holdings of Riley and Carpenter dictate that cell phones and similar electronics cannot be searched without a warrant, even under the automobile exception.”); see also Bryan Sandford, A Castle in the Sky: GPS Tracking of A Defendant’s Cell Phone Post-Riley v. California, 2015 Wis. L. Rev. 907, 910 (2015) (“[A] broad reading of Riley is the logical extension of the Court’s Fourth Amendment jurisprudence.”).

37. Riley, 573 U.S. at 375.