Does the Fourth Amendment Prohibit Warrantless GPS Surveillance?

Does the Fourth Amendment require a warrant to conduct surveillance of a government-installed GPS device, such as a device installed on a suspect’s car to monitor the car’s location? This issue comes up occasionally, and the DC Circuit has a case pending on the issue. I don’t think I have ever blogged about it, so I want to offer my thoughts. This post will explain why I think the doctrine here was settled by a pair of Supreme court cases from the 1980s, and why those cases draw a pretty reasonable Fourth Amendment line.

I. Supreme Court Precedents: Knotts and Karo

In the 1980s, the Supreme Court decided two cases on whether the Fourth Amendment requires a warrant for the government to monitor a suspect’s location using a government-installed locating device. Both cases involved beepers, defined as “a radio transmitter, usually battery-operated, which emits periodic signals that can be picked up by a radio receiver.” The combined holding of United States v. Knotts, 460 U.S. 276 (1983), and United States v. Karo, 468 U.S. 705 (1984), was that the constitutionality of warrantless beeper surveillance depends on what information the beeper reveals. Beeper surveillance that reveals the location of the beeper in a public place does not require a warrant (Knotts); on the other hand, beeper surveillance that reveals the location of the beeper inside a home does require a warrant (Karo).

The Court did leave open the door to a different approach, however. In the first of these two cases, Knotts, the Supreme Court addressed the concern that the power to conduct public surveillance using beepers might allow “dragnet-type law enforcement.” Then-Justice Rehnquist suggested that abuses occurring under the Court’s rule might justify a different result:

[The Defendant] expresses the generalized view that the result of the holding sought by the Government would be that “twenty-four hour surveillance of any citizen of this country will be possible, without judicial knowledge or supervision.” Brief for Respondent 9. But the fact is that the reality hardly suggests abuse; if such dragnet-type law enforcement practices as respondent envisions should eventually occur, there will be time enough then to determine whether different constitutional principles may be applicable.

II. Is GPS Different? The Lower Court Cases

Fast-forward 25 years, and the new issue is how Karo and Knotts apply to the use of GPS devices. The basic issue is whether GPS devices are so different from beepers that their use amounts to “dragnet-type law enforcement practices,” allowing courts to distinguish Knotts and regulate the use of public-revealing GPS devices.

In a law review article published in 2007, lawprof Renee Hutchins made such a case. She argued that GPS locating devices should be treated different from beeper locating devices because the technology has the ability to be much more invasive. GPS devices can be used more easily, more cheaply, and work more effectively at determining location than can beepers. So far, however, courts have rejected such arguments. Some state courts have regulated GPS surveillance under state constitutions, but no court (that I’m aware of) has held that the federal Fourth Amendment regulates public location information obtained from GPS devices. The only federal circuit to answer the question rejected the challenge in United States v. Garcia, 474 F.3d 994 (7th Cir. 2007) (Posner, J.).

A few weeks ago, however, the DC Circuit held oral argument in a case raising these issues in which the panel seemed open to a different result: The Blog of Legal Times reported:

Peter Smith, an assistant U.S. attorney in the District of Columbia, argued that the authorities did not need a warrant to attach the global positioning system onto the vehicle of the suspect, Antoine Jones, the target of a cocaine trafficking ring in Washington. Jones was convicted last year and sentenced to life in prison. He is challenging the conviction.
The government’s position generated a lively discussion in the appeals court, where Judges David Tatel, Douglas Ginsburg and Thomas Griffith debated the extent to which a person has a reasonable expectation of privacy while driving on public roads. The panel appeared concerned about the lack of judicial supervision. Oral argument lasted more than an hour, far longer than the time allotted to the case. There was no immediate ruling.
Ginsburg said the fact the government got a warrant the first time suggests the government believed a warrant was required. Investigators secretly recorded the movement of Jones’ vehicle for a month before he was arrested in October 2005. “We’re not talking about one day here. We’re talking about a month,” Griffith said.
. . . Tatel noted what he called the “big caveat” in Knotts. The late Justice William Rehnquist said in Knotts that if 24-hour surveillance were ever implemented, “[t]here will be time enough then to determine whether different constitutional principles may be applicable. The Jones case, Tatel said, presents that scenario.

We don’t know where the DC Circuit is going in the Jones case, but it seems possible that the panel might rule that GPS surveillance is constitutionally different from beeper surveillance and that a different rule must be applied.

III. Why Knotts/Karo Cover GPS Cases

My own view is that lower courts must follow the Knotts/Karo line in GPS cases, and that they are not free to adopt a different approach based on the potential capabilities of GPS surveillance. To see why, it helps to step back and situate Karo and Knotts in the body of Fourth Amendment law.

Karo and Knotts both adopt what I have called the “private facts” approach to the Fourth Amendment. This approach is used widely in the high-tech setting, and it bases the legal rule on the category of information obtained: Some information gets protected and other information does not, with the Supreme Court saying which is which. When the Supreme Court adopts this approach, the key question is the nature of the information collected instead of the details of the technology used to collect it. So, for example, a device used to detect the presence of illegal drugs that can only reveal whether drugs are present is outside the Fourth Amendment regardless of whether the “device” is a trained police dog or a chemical test. The details of the technology don’t matter: what matters is the information actually collected.

The private facts approach is very useful in the high-tech setting because technology is a moving target. Surveillance Tool 1.0 is quickly replaced by Tool 1.1 and then 1.2. The Supreme Court can’t possibly decide a new case every time the tool changes. Indeed, if the legal rule hinged on the details of the technology, no one would ever know when the technology changed just enough to result in a different rule. The private facts approach lets the Supreme Court adopt a rule that remains certain and clear as technology advances: The trigger remains the information collected, regardless of the technology used to collect it. That way the Supreme Court can devise a constitutional line and have lower courts enforce that line over time.

In light of this understanding, I don’t think it makes any difference whether location information is obtained using a beeper or a GPS device. The Supreme Court has announced the line for location devices, and lower courts have to enforce that line regardless of the details of the technology. The fact that GPS devices have the potential to be used or abused in ways more invasive than beepers doesn’t let lower courts adopt a different rule for them. Indeed, the Supreme Court emphasized the difference between potential and actual abuses in both Karo and Knotts. In Karo, that point was made was in the Court’s reminder that “[i]t is the exploitation of technological advances that implicates the Fourth Amendment, not their mere existence.” In Knotts, that point was made in the passage quoted near the top of the case about the potential for dragnet surveillance. As I read that passage, the key point was that an actual abuse had to occur to raise the possibility of treating abuses differently: mere potential for abuses did not justify a different rule. It seems to me that the GPS device used in the Jones case collected essentially the same information that was collected in Knotts, and did not involve abuses. It therefore should be covered by the Knotts rule.

IV. Why the Knotts/Karo Line Is a Reasonable One

Some readers may be thinking, “But wait, Knotts is wrong!” As a result, they may want the courts to do anything that helps limit Knotts or even plant the seeds of its overruling. That raises the more fundamental question of whether the future Supreme Court should stick with Knotts/Karo or adopt a different rule.

To answer this, it help to see Knotts and Karo as examples of a recurring question of Fourth Amendment law: How to adapt the inside/outside distinction in light of new technologies? As I argue in this article, the inside/outside distinction is the basic building block of the Fourth Amendment. Surveillance of open spaces does not trigger the Fourth Amendment, while surveillance that breaks into enclosed spaces does. This dividing line ordinarily gives the government the power to investigate open spaces but not enclosed ones. The key question is how or whether to apply this line when technology changes: If technology allows greater surveillance, should the Supreme Court move the Fourth Amendment line accordingly? Karo and Knotts update the old line in a way that retains the basic inside/outside distinction. The cases look to whether the information collected reveals information about the inside of the home or what is happening outside, treating the locating device as a virtual person who either enters the home or stays outside it.

I think that’s a reasonable choice, as it aims for technology neutrality. It’s the basic approach I advocate in applying the Fourth Amendment to the Internet. It’s not perfect, of course. In my view, it should also be supplemented by statutory privacy laws to regulate the use of GPS devices, much like existing statutory privacy law presently regulates location information for cell phones. Statutory privacy laws have the advantage of flexibility: They could adopt a mid-level standard such as “reasonable suspicion” to regulate GPS surveillance and deter abuses, something that is much harder to get from the Fourth Amendment (which ordinarily requires a warrant).

Finally, if you reject Knotts and the inside/outside line, you need to come up with a replacement. It’s easy to say that you think the Fourth Amendment should regulate GPS surveillance. But it’s much harder to come up with a general view as to how the Fourth Amendment should regulate public surveillance and then situate the case of GPS within it. It’s not impossible, but it’s much harder. It’s especially difficult for a group of Justices to agree on another line that could operate with a reasonable degree of clarity in a range of cases over time. So while Knotts/Karo do not provide the only line the Court could follow, I think they do offer a reasonable one.