The federal government conducted a search for purposes of the Fourth Amendment when it attached a GPS tracking device to a suspect’s car and used the device to track the suspect’s movements for 28 days, the U.S. Supreme Court ruled Monday.

All nine justices voted to uphold the decision by the U.S. Court of Appeals for the D.C. Circuit reversing Antoine Jones’s drug-trafficking conviction, which was partly based on evidence obtained from the tracking device. But the Court split 5-4 on how the government’s actions constituted a search within the meaning of the Fourth Amendment.

A five-justice majority, in an opinion written by Justice Antonin Scalia, held that the government’s physical attachment of the device to Jones’s car was the critical factor because the Fourth Amendment specifically protects “the right of the people to be secure in their persons, houses, papers, and effects, against unreasonable searches and seizures.”  Physically trespassing on one of Jones’s “effects” — the car — in order to obtain information would have been considered a search when the Fourth Amendment was adopted, the Court held, and such an intrusion therefore requires the government to obtain a warrant under most circumstances. Chief Justice John Roberts and Justices Anthony Kennedy, Clarence Thomas and Sonia Sotomayor joined Justice Scalia’s majority opinion.

In Jones’s case, the government had obtained a warrant but had not followed the warrant’s directions requiring that the GPS device be attached to Jones’s car in the District of Columbia within 10 days after the warrant was issued. The government argued it could track Jones’s car without a warrant because Jones’s movements on public roads were visible to all, and thus Jones could have no reasonable expectation of privacy in those movements.  The “reasonable expectation of privacy” standard has been a cornerstone of Fourth Amendment analysis since the Supreme Court’s 1967 ruling in Katz v. United States, in which the Court held that attaching an eavesdropping device to a public phone booth could be a search governed by the Fourth Amendment even if the government did not physically intrude on the defendant’s property. Prior to Katz, the Court’s Fourth Amendment rulings had focused on physical trespasses.

In Monday’s ruling, the Court concluded that “Jones’s Fourth Amendment rights do not rise or fall with the Katz formulation,” holding instead that “the Katz reasonable-expectation-of-privacy test has been added to, not substituted for, the common-law trespassory test.” The Court held that, although the Fourth Amendment may govern searches that involve no physical trespass, when “the Government obtains information by physically intruding on a constitutionally protected area, such a search has undoubtedly occurred.”  The Court additionally affirmed the D.C. Circuit’s decision that because the government failed to argue that the search was reasonable, attaching the GPS device violated the Fourth Amendment in this case. 

In an opinion concurring only in the judgment, Justice Samuel Alito criticized the majority’s reliance on “18th-century tort law” as “strain[ing] the language of the Fourth Amendment,” “highly artificial,” and lacking support in post-Katz case law.  Justice Alito, joined by Justices Ruth Bader Ginsburg, Stephen Breyer and Elena Kagan, would have reached the same result by applying Katz to find that “the use of longer term GPS monitoring in investigations of most offenses impinges on expectations of privacy” because “society’s expectation has been that law enforcement agents and others would not — and indeed, in the main, simply could not — secretly monitor and catalogue every single movement of an individual’s car for a very long period” due to the practical challenges involved. While it may be difficult for judges to draw a line governing how long surveillance can continue before violating the Fourth Amendment, “[w]e need not identify with precision the point at which the tracking of this vehicle became a search, for the line was surely crossed before the 4-week mark.”

Justice Alito’s opinion highlighted “the emergence of many new devices that permit the monitoring of a person’s movements,” particularly modern cell phones, and noted that “[i]n circumstances involving dramatic technological change, the best solution to privacy concerns may be legislative.” That was how complex questions surrounding wiretapping ultimately were resolved, the opinion noted. Congress enacted a comprehensive wiretapping statute in reaction to Katz, and since then the statute has been the primary source of law on the subject. But Congress and most states have not yet passed laws governing police use of GPS tracking. Two companion bills pending in Congress — one in the House, one in the Senate — would address that issue, but neither has made it out of committee.

By basing its ruling on the government’s physical trespass on Jones’s car, the majority avoided addressing whether the long-term tracking of an individual’s movements would by itself constitute a search within the meaning of the Fourth Amendment. The Court did stress that such surveillance would be judged under the Katz reasonable-expectation-of-privacy test, a point amplified in Justice Sotomayor’s separate concurrence. However, it was not yet necessary to resolve those questions because the majority’s narrower approach was enough to resolve Jones’s case, Justice Sotomayor wrote.