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Federal and state law enforcement officials throughout the nation are currently using Global Positioning System (GPS) technology for automated, prolonged surveillance without obtaining warrants. As a result, cases are proliferating in which criminal defendants are challenging law enforcement’s warrantless uses of GPS surveillance technology, and courts are looking for direction from the Supreme Court. Most recently, a split has emerged between the Ninth and D.C. Circuit Courts of Appeal on the issue. In United States v. Pineda-Moreno, the Ninth Circuit relied on United States v. Knotts — which approved the limited use of beeper technology without a warrant — to uphold warrantless use of GPS surveillance technology. However, in United States v. Maynard, the D.C. Circuit held that warrants are required for law enforcement use of GPS tracking devices. In distinguishing Knotts, the D.C. Circuit pointed to the vast differences between the relatively primitive beeper technology used almost thirty years ago and the unprecedented power of GPS surveillance technology used today. The Seventh Circuit Court of Appeals and various state courts are similarly divided. In light of this confusion, the Supreme Court has recently agreed to review the issue, granting certiorari from the decision of the D.C. Circuit in Maynard and leaving the Pineda-Moreno petition in a holding pattern. On November 8, the Supreme Court will hold oral arguments in the case, which was docketed under the new name United States v. Jones.

The Supreme Court’s Fourth Amendment doctrine, including its cases evaluating new surveillance technologies, has always been informed by one of the Amendment’s animating principles: its mandate to prevent abuse of police power. While the Court has not always articulated this theory of the Fourth Amendment as clearly as it could have, a careful review of the case law reveals a concern about abuse and “a too permeating police surveillance.” This reading demands that, in any review of new surveillance technology, courts must evaluate the technology’s potential for abuse. Unfortunately, in drawing lines between technology such as powerful binoculars that merely enhance the senses of law enforcement officials and technology such as thermal imaging devices that create new superhuman powers, the Justices have offered confusing guidance to lower courts. At times, they have relied on a distinction between sense enhancement and sense creation, a superficial distinction that fails to delineate when new surveillance technology is problematic. At other times, the Court has reverted to language reminiscent of past Fourth Amendment doctrine requiring some sort of physical trespass in order to trigger the warrant requirement. The Court rejected that doctrine in Katz v. United States, when it recognized that new technologies make a private space/public space line unworkable. However, the Justices’ failure to explain clearly the source of their concerns about new technology, coupled with their haphazard use of language, has confused the lower courts and commentators. This confusion has led some to conclude that the use of GPS surveillance technology for prolonged, automated surveillance of targets should not be considered a “search” subject to the Fourth Amendment, at least to the extent that the surveillance occurs on public streets. As we argue in this Essay, the use of GPS surveillance for prolonged monitoring without a warrant cannot pass muster under the Fourth Amendment. It may seem at first glance that GPS tracking of public actions — actions that the police can otherwise follow without a warrant in the status quo — is harmless from a privacy perspective. After all, if cops can tail a suspect for days or weeks without a warrant, what difference does it make if the tracking is done by an undercover officer or a GPS device under the hood of a suspect’s car? However, when “machines are watching” — that is, when tracking is automated and extended for prolonged periods of time — the potential for abuse grows larger. In such circumstances, the warrant requirement, with its limited exceptions, provides a necessary check on overreach by law enforcement authorities.

This Essay is organized in three Parts. In Part I, we outline the Fourth Amendment’s structural protections against law enforcement abuse and explain the Court’s historic approach to new surveillance technologies. While the Court’s approach is undertheorized, we show that the Court has carefully examined new technologies to prevent technological end-runs around existing legal doctrine that seeks to protect personal privacy. We maintain that the Court’s doctrinal distinction between sense-enhancing and sense-creating technology is effectively a proxy for the Court’s underlying interest in protecting against governmental abuse. In Part II, we explain why GPS surveillance technology creates unprecedented potential for abuse, and we present anecdotal evidence suggesting that abuse of GPS surveillance technology may be occurring already. Note, though, that our argument does not hinge on the claim that abuse is widespread. Rather, we argue that GPS surveillance poses a real threat, even if (and we have no way of knowing whether this is true) the potential for abuse has not yet been realized except in a limited number of cases. Our conception of the Fourth Amendment differs fundamentally from the Solicitor General’s view, expressed in the government’s brief in Jones, that “[t]he decision whether to apply different constitutional principles to hypothetical programs of mass, suspicion- less surveillance can await resolution if such programs ever occur.” We do not believe that the Court must stand aside until “Big Brother” arrives; doing so would render the Fourth Amendment’s protections a “dead letter.”

In Part III, we connect our interpretation of the Fourth Amendment to the “reasonable expectation of privacy” language that looms large in contemporary case law. In our view, a “reasonable expectation of privacy” may be violated even if individuals already anticipate that the information at issue can be accessed by law enforcement officials. Indeed, any other interpretation of that language would yield perverse implications: if “hypothetical programs of mass, suspicion-less surveillance” ever arrived, individuals would then have no expectation of privacy once they learned of the surveillance, and the “expectation of privacy” protection — if interpreted literally — would become a nullity.

Our interpretation of the Fourth Amendment is consistent with the concerns underlying past Supreme Court decisions. As Part III explains, control over information about our location is still central to our sense of self. This interpretation of the Fourth Amendment and the individual rights interpretation ultimately converge in GPS cases, and both views counsel in favor of the conclusion that the use of this technology for automated, prolonged surveillance should be subject to the Fourth Amendment’s warrant requirement.