by Hogan Paschal*

Does warrantless, prolonged location tracking violate the Fourth Amendment’s protections against unreasonable searches? Hogan Paschal (’17) examines this question, based on her experience at the 2016 Spong Moot Court Tournament, hosted by William & Mary Law School on February 12-13th, 2016. The location tracking tools employed by Government investigators have become more sophisticated and widespread, often eroding the practical constraints that government resources previously imposed on search power. This Contribution posits a more holistic reading of the Fourth Amendment, that simultaneously acknowledges its historical context and modern investigative challenges. Ultimately, it argues that courts should restore Fourth Amendment safeguards by requiring a warrant as a precursor to the government’s use of prolonged location tracking.

With increasing frequency, government entities throughout the United States are harnessing the investigative power of location tracking, including scanning license plates, collecting cell tower data, and using GPS technology.2 Frequently, the government conducts this surveillance for prolonged periods of time, continuously, and without a warrant. Courts are grappling with the constitutionality of prolonged, surreptitious location tracking. Most recently, the Supreme Court dealt with the issue in United States v. Jones, a case in which the government attached a GPS tracking device to a person’s car for twenty-eight days.3 In order to check against the increased potential for government abuse of this search power, courts must develop and apply Fourth Amendment protections appropriate for a new technological age.

Advocates of warrantless location tracking argue that, because GPS captures only a person’s movements in public, the practice is constitutional, as the Fourth Amendment does not protect that which a person knowingly discloses to the public. Rather, they would contend that the Fourth Amendment protects only that which a person can attribute a reasonable expectation of privacy.

However, this argument presumes that the Fourth Amendment is exclusively and entirely aimed at protecting privacy. It is not. The Fourth Amendment was designed to check government power. The Framers drafted the Amendment in response to the wholly unbounded search power of the British government. Chief Justice Roberts recently observed:

Our cases have recognized that the Fourth Amendment was the founding generation’s response to the reviled “general warrants” and “writs of assistance” of the colonial era, which allowed British officers to rummage through homes in an unrestrained search for evidence of criminal activity. Opposition to such searches was in fact one of the driving forces behind the Revolution itself.4

In practice, the Fourth Amendment restrains government search power through its warrant requirement, which imposes a judicial check on the executive branch’s power to search.5

Protection from unlimited government search power does not end with the Fourth Amendment. For most of our history, practical limits complemented the constitutional protections of the warrant requirement.6 For example, before the advent of smart phones, a police officer’s search of a person was practically limited to that which would fit in a person’s pockets, thus constraining an officer’s search discretion. The storage capacity of a person’s pockets is incredibly more limited than that of a cloud-connected smartphone within that pocket.7 In this way, constitutional and practical protections worked in tandem to curtail government search power.8 Technological developments have dissolved these practical constraints and “erode[d] the privacy guaranteed by the Fourth Amendment.”9 When such erosion occurs, the Court generally restores the protection previously provided by practical constraints by requiring a warrant, as it did with smartphones in Riley v. California.


By providing the government with extrasensory abilities, prolonged location tracking similarly eliminates practical checks on government power in two ways. First, extrasensory technology does not merely enhance normal human perception; it also overcomes limitations imposed by the five senses.10 For example, in United States v. Kyllo, warrantless police use of infrared imaging technology allowed police to perceive heat being given off by the home.11 Without the technology, the police would have been unable to perceive the excess heat being given off by the defendant’s marijuana-growing operation. Because the technology provided such extrasensory information, the Court held that the warrantless use of the technology in the context of the home violated the Fourth Amendment; the Court thereby restored the check previously provided by the limitations of human eyesight.

Additionally, by aggregating a person’s GPS location data, the government can harvest highly intimate personal details that any discrete data point would not otherwise reveal.12 For example, computer scientists can utilize algorithms and statistical analyses to predict a person’s gender, marital status, occupation, and age based on as little as one week’s worth of GPS location history.13 Just as the thermal imagery technology at issue in Kyllo allowed an observer to gather information about a home that would not otherwise be available, so can aggregated location surveillance translate a person’s weekly travels into sensitive personal data. In these ways, extrasensory technology expands the scope of the government’s power to search.

Second, prolonged location data erodes the practical constraint that government resources previously imposed on search power. Location tracking can produce an astonishing volume of information at very little cost to the government. Before location-tracking technology was available, law enforcement would have had to use human surveillance to continuously track a person’s location. Such surveillance would have required an enormous amount of resources, and would likely only occur if the investigation was of unusual importance.14 In other words, the expense of prolonged location surveillance limited the frequency and length of the government’s search power. However, when technology eliminates the costs of surveillance, the government’s power to search becomes more extensive. The erosion of this practical constraint presents huge potential for abuse, as Justice Sotomayor recognized in her own Jones concurrence: “[T]he Government’s unrestrained power to assemble data that reveal private aspects of identity is susceptible to abuse. The net result is that GPS monitoring—by making available at a relatively low cost such a substantial quantum of intimate information about any person whom the Government, in its unfettered discretion, chooses to trace—may alter the relationship between citizens and government in a way that is inimical to democratic society.”15


Because prolonged GPS tracking erodes the aforementioned practical constraints, the government’s use of such technology facilitates wholly unchecked search power, which the Fourth Amendment should preclude. This is true even under the Court’s current test of “reasonable expectations of privacy” established in Katz v. United States: a person may reasonably expect that location tracking might reveal where that person has traveled in public, but a person certainly does not reasonably expect that this location data, in the aggregate, will reveal personal details such as sexual orientation or medical ailments.16

Courts must restore these safeguards by requiring a warrant—and the judicial oversight accompanying it—for the government’s use of prolonged location tracking. Otherwise, the courts invite the development of a surveillance state in which law enforcement makes end runs around the Fourth Amendment by assembling public information to discover highly sensitive private information. The Constitution simply cannot stand for such an Orwellian alternative.

* This piece is the author’s commentary on one of the questions presented at the 2016 Spong Constitutional Law Moot Court Tournament held at the William & Mary School of Law in Williamsburg, Virginia. The issue at heart of the problem was whether warrantless, prolonged location tracking violated the Fourth Amendment. The views expressed in this article do not necessarily represent the views of the author on this point of law. Rather, this article is a distillation of one side of an argument, which the author represented.

2. See You Are Being Tracked, American Civil Liberties Union, (last visited Apr. 24, 2016) (license plate scanners); United States v. Jones, 132 S. Ct. 945 (2012) (GPS tracking); United States v. Davis, 785 F.3d 498, 519 (11th Cir.), cert. denied, (2015) (cell tower data).

3. In 2011, the Supreme Court considered whether GPS tracking constituted a Fourth Amendment search. Jones, 132 S. Ct. at 947. In that case, the government attached a GPS tracking device to the underside of a suspect’s car and tracked the suspect’s location for 28 days without pause. Id. The Court held that the government’s surveillance violated the Fourth Amendment, because attaching the tracking device was a physical trespass. Id. at 954. The Court left open the question of whether prolonged GPS tracking, absent a physical trespass, is a Fourth Amendment search. Id. at 964 (Alito, J., concurring).

4. Riley v. California, 134 S. Ct. 2473, 2494 (2014). See also Fabio Arcila, Jr., Death of Suspicion, 51 Wm. & Mary L. Rev. 1275, 1284 (2010) (“The Framers’ key concern behind their desire to ban general warrants and writs of assistance was to limit search discretion.”) (internal citations omitted); Renée McDonald Hutchins, Tied Up in Knotts? GPS Technology and the Fourth Amendment, 55 UCLA L. Rev. 409, 444 (2007) (“The Fourth Amendment, at its core, regulates police conduct.”).

5. Riley, 134 S. Ct. at 2482 (internal citations omitted). See also United States v. Karo, 468 U.S. 716, 717 (1984) (“Requiring a warrant will have the salutary effect of ensuring that use of [surveillance technology] is not abused, by imposing upon agents the requirement that they demonstrate in advance their justification for the desired search.”); Katz v. United States, 389 U.S. 347, 357 (1967) (“[T]he Constitution requires that the deliberate, impartial judgment of a judicial officer [in issuing a warrant] . . . be interposed between the citizen and the police.”) (internal citations omitted).

6. See, e.g., Jones, 132 S. Ct. at 963 (Alito, J., concurring) (“In the pre-computer age, the greatest protections of privacy were neither constitutional nor statutory but practical.”).

7. See Riley, 134 S. Ct. at 2478 (“Before cell phones, a search of a person was limited by physical realities and tended as a general matter to constitute only a narrow intrusion on privacy.”).

8. See, e.g., Jones, 132 S. Ct. at 963 (Alito, concurring).

9. Kyllo v. United States, 533 U.S. 27, 35 (2001)

10. See generally Hutchins, supra note 4, at §II(C). For example, compare binoculars with infrared imaging technology. Binoculars magnify human sight, but do not reveal anything otherwise imperceptible to normal vision. On the other hand, infrared imaging technology allows a person to effectively see through walls. See Kyllo, at 29–30. Binoculars are sense-enhancing, whereas infrared imaging is extra-sensory.

11. 533 U.S. at 40.

12. See, e.g., United States v. Maynard, 615 F.3d 544, 562 (D.C. Cir. 2010) (“Prolonged surveillance reveals types of information not revealed by short-term surveillance, such as what a person does repeatedly, what he does not do, and what he does ensemble. These types of information can each reveal more about a person than does any individual trip in isolation.”), aff’d in part sub nom. United States v. Jones, 132 S. Ct. 945 (2012); People v. Weaver, 12 N.Y.3d 433, 442 (N.Y. 2009) (noting prolonged location monitoring “yields . . . a highly detailed profile, not simply of where we go, but by easy inference, of our associations—political, religious, amicable and amorous, to name only a few—and of the pattern of our professional and avocational pursuits.”)

13. See, e.g., Sanja Brdar, Dubravko Culibrk & Vladimir Crnojevic, Demographic Attributes Prediction on the Real-World Mobile Data, Mobile Data Challenge 2012 (by Nokia) Workshop, (last visited Apr. 24, 2016); Steven M. Bellovin, et al., When Enough is Enough: Location Tracking, Mosaic Theory, and Machine Learning, 8 N.Y.U. J.L. & Liberty 555, 557–558 (2014).

14. 132 S. Ct. at 963–64 (Alito, J., concurring) (“Traditional surveillance for any extended period of time was difficult and costly and therefore rarely undertaken . . . Only an investigation of unusual importance could have justified such an expenditure of law enforcement resources.”) (internal citations omitted).

15. Id. at 956 (Sotomayor, J., concurring) (internal citations omitted).

16. See Katz, 389 U.S. at 361 (Harlan, concurring); Maynard, 615 F.3d at 562.