On January 23, 2012, the Supreme Court decided United States v. Jones, No. 10-159, holding that the government's use of a Global Positioning System (GPS) device to track the movements of an individual's automobile constitutes a search within the meaning of the Fourth Amendment.
In 2005, the FBI suspected Antoine Jones of participating in a narcotics trafficking conspiracy. Agents installed a GPS tracking device on the undercarriage of the Jeep that Jones was driving while it was parked in a public parking lot. Over the next 28 days, by means of signals from multiple satellites, the government tracked the location of Jones's vehicle. Prosecutors ultimately used the information gleaned from the GPS device to prosecute Jones for conspiracy to distribute cocaine.
Jones moved to suppress the data about his movements, but the district court denied the motion in large part because, under the precedent of United States v. Knotts, 460 U. S. 276, 281 (1983), a person traveling in an automobile on public thoroughfares "has no reasonable expectation of privacy in his movements from one place to another." The United States Court of Appeals for the District of Columbia Circuit reversed, holding that the warrantless use of the GPS tracking device violated the Fourth Amendment.
The government petitioned for certiorari, and the Supreme Court unanimously affirmed. The Court held that the government's installation of a GPS device on a target's vehicle and its use of that device to monitor the vehicle's movements constituted a "search" under the Fourth Amendment. It rested its decision on the principle that the government's act of installing the GPS tracking device on the undercarriage of the Jeep constituted a "physical intrusion" that would have been considered a search when the Fourth Amendment was adopted. Because an automobile is indisputably an "effect" protected under the Fourth Amendment, and the installation was an intrusion into that effect, the Court held that a "search" within the meaning of the Fourth Amendment had occurred. The Court held that the well-known "reasonable expectation of privacy" test derived from Katz v. United States, 389 U.S. 347 (1967), added to, but did not substitute for, the common-law trespassory test.
In two separate concurrences, five Justices addressed issues of whether and how, in Justice Sotomayor's words, "the same technological advances that have made possible nontrespassory surveillance techniques will also affect the Katz test by shaping the evolution of societal privacy expectations," but disagreed on the answers to those questions. The Court's actual decision left authoritative resolution of those questions for another day and instead relied upon the non-consensual physical placement of the tracking device on the automobile. Nevertheless, the concurrences suggested that five of the Justices viewed GPS usage under the facts of this case as violating an individual's reasonable expectation of privacy.
Justice Scalia delivered the opinion for the court, in which Chief Justice Roberts and Justices Kennedy, Thomas, and Sotomayor joined. Justice Sotomayor wrote a concurring opinion. Justice Alito wrote an opinion concurring in the judgment, in which Justices Ginsburg, Breyer, and Kagan joined.