In United States v. Jones, five Supreme Court Justices wrote that government surveillance of one’s public movements for twenty-eight days using a GPS device violated a reasonable expectation of privacy and constituted a Fourth Amendment search. Unfortunately, they didn’t provide a clear and administrable rule that could be applied in other government surveillance cases. In this Essay, Kevin Bankston and Ashkan Soltani draw together threads from the Jones concurrences and existing legal scholarship and combine them with data about the costs of different location tracking techniques to articulate a cost-based conception of the expectation of privacy that both supports and is supported by the concurring opinions in Jones.
As Judge Richard Posner once said, “Technological progress poses a threat to privacy by enabling an extent of surveillance that in earlier times would have been prohibitively expensive,” thereby “giving the police access to surveillance techniques that are ever less expensive and ever more effective.”2 Among these “‘fantastic advances’”3 in surveillance technology is the Global Positioning System (GPS), which provides law enforcement with an inexpensive means to track the precise geographic locations of criminal suspects. The Supreme Court recently addressed this technology in United States v. Jones, which considered whether the police’s attachment of a GPS device to a suspect’s car, and the use of that device to monitor the car’s movements along public roads for twenty-eight days, constituted a search under the Fourth Amendment.4
All nine Justices answered that question in the affirmative, but they produced three different opinions. Five Justices, in an opinion authored by Justice Scalia, did not rule on the question of whether the monitoring of Jones’s movements via the GPS device constituted a search. Rather, the majority found that the attachment of the device to Jones’s car violated his Fourth Amendment expectation of privacy under a trespass-oriented theory of Fourth Amendment protection.5 Four other Justices signed a concurring opinion by Justice Alito, rejecting the majority’s trespass theory and arguing that the prolonged monitoring of the GPS device constituted a search by violating Jones’s expectation of privacy.6 And finally, Justice Sotomayor both joined the majority opinion and wrote her own concurring opinion, agreeing with the majority that the installation constituted a search but also agreeing with Justice Alito that “‘longer term GPS monitoring in investigations of most offenses impinges on expectations of privacy.’”7
The Jones concurrences, taken together, are potentially a watershed moment in the Court’s Fourth Amendment jurisprudence. Prior to Jones, the Court’s precedent on location tracking—regarding radio “beeper”-based vehicle tracking in the 1980s—indicated that one could have no reasonable expectation of privacy in one’s public movements.8 In Jones, five Justices rejected that proposition, at least with respect to prolonged government surveillance of one’s public movements. Unfortunately, those Justices stopped short of clarifying when one does have such an expectation or when surveillance violates it—other than Justice Alito’s conclusion that “the line was surely crossed before the 4-week mark.”9
Trying to make sense of the Jones concurrences and reduce them to a clear and administrable rule—or, alternatively, arguing that they make no sense and cannot be so reduced—has become something of a cottage industry amongst privacy law scholars.10 Building on the work of those who have come before us, this Essay is our attempt to make sense—and “cents”—out of United States v. Jones, by demonstrating how new technologies are continually reducing the cost of surveillance and by attempting to formulate a new approach to defining the Fourth Amendment’s protections based on those falling costs.
Specifically, we propose that a new surveillance technique is likely to violate an expectation of privacy when it eliminates or circumvents a preexisting structural right of privacy and disrupts the equilibrium of power between police and suspects by making it much less expensive for the government to collect information. We explain how courts might put that general proposition into practice by using estimates of the actual costs of particular modes of location tracking to apply a rough rule of thumb: if the new tracking technique is an order of magnitude less expensive than the previous technique, the technique violates expectations of privacy and runs afoul of the Fourth Amendment.
Although we derive this approach from the specific example of location tracking and limit our Essay to that topic, we are hopeful that it may also prove a useful tool in evaluating other surveillance techniques.
By Kevin S. Bankston and Ashkan Soltani
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