The Supreme Court unanimously held Monday that the installation of a GPS device in a person's car constitutes a "search" under the Fourth Amendment (which prohibits "unreasonable searches and seizures”). This unanimity is somewhat misleading, however, as the Court split with respect to what theory of the Fourth Amendment should be applied going forward and left a crucial question unanswered.
The Court has often struggled to adapt the Fourth Amendment to technologies that expand the reach of the state. As is reflected in the amendment’s language ("The right of the people to be secure in their persons, houses, papers, and effects") government searches at the time of the amendment's adoption generally involved the physical invasion of property. But various technological innovations have allowed the state to increase its surveillance authority without conducting physical searches, and the Supreme Court has sometimes been behind the curve. In the 1928 case Olmstead v. United States , most famous for Justice Louis Brandeis's dissenting opinion that the Bill of Rights "conferred, as against the Government, the right to be let alone—most comprehensive of rights, and the right most valued by civilized men," the Court upheld the warrantless wiretapping of a suspect's phone. Recognizing that the focus on physical searches was inadequate, however, in Katz v. United States (1967) the Court held that warrantless eavesdropping on conversations at a public phone booth violated the Fourth Amendment. As Justice John Marshall Harlan wrote in his influential concurrence in Katz, the Fourth Amendment applies wherever an individual "has a constitutionally protected reasonable expectation of privacy."
The split on the Court Monday, in essence, focused on which of these strands of Fourth Amendment jurisprudence to emphasize. The most interesting opinion in the case, however, is Justice Sonia Sotomayor's concurrence. Although I'm a little puzzled as to why she joined Justice Antonin Scalia's opinion—which seems to give less attention to her fundamental concerns—her own analysis is brilliant, forcefully arguing that the Court needs to rethink its Fourth Amendment jurisprudence in light of the Internet/wireless communication age. The "expectation of privacy" standard will not provide adequate protection if the increased potential power of the state is not taken into account. Sotomayor is correct, first of all, to argue, that "it may be necessary to reconsider the premise that an individual has no reasonable expectation of privacy in information voluntarily disclosed to third parties." And she is extremely persuasive in her argument about why the judiciary needs to check the use of GPS technology:
Awareness that the Government may be watching chills associational and expressive freedoms. And the 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 track—may “alter the relationship between citizen and government in a way that is inimical to democratic society.” [...] I would take these attributes of GPS monitoring into account when considering the existence of a reasonable societal expectation of privacy in the sum of one’s public movements. ... I would also consider the appropriateness of entrusting to the Executive, in the absence of any oversight from a coordinate branch, a tool so amenable to misuse, especially in light of the Fourth Amendment’s goal to curb arbitrary exercises of police power to and prevent “a too permeating police surveillance.”
Justice Scalia's opinion for the majority, while accepting Katz, rests on the fact that the installation of a GPS device is a physical invasion of property and hence violates the Fourth Amendment as it was originally understood. Justice Alito's concurrence—joined, in an unusual coalition, by Justices Ruth Bader Ginsburg, Stephen Breyer, and Elena Kagan—argues that it is strained to argue that the installation of a GPS tracking device to the bottom of a vehicle is a "search" as originally understood, and instead the proper standard is whether the GPS tracking violates the "reasonable expectation of privacy" standard. "The Court’s reasoning," Alito argues, "largely disregards what is really important (the use of a GPS for the purpose of long-term tracking) and instead attaches great significance to something that most would view as relatively minor (attaching to the bottom of a car a small, light object that does not interfere in any way with the car’s operation)." This is an important point, as the majority opinion would seem to place no constraint on GPS searches that don't require attaching a physical device to a private car. Taking into account factors such as the long-term nature of the tracking, Alito argues, the use of monitoring in this case must be considered a "search."
While these disagreements may seem technical, what theory the Court uses is very important going forward. This is particularly true because while the Court was unanimous in holding that the state's actions here constituted a "search," it did not address the question of whether this search was "reasonable." The apparent victory for civil liberties in this case will be a hollow one if the Court declares GPS tracking without a valid warrant a "search" but then carves it exceptions that make most such searches "reasonable." For the points eloquently stated by Justice Sotomayor, this would be the wrong approach.