WASHINGTON — The Supreme Court on Monday ruled unanimously that the police violated the Constitution when they placed a Global Positioning System tracking device on a suspect's car and monitored its movements for 28 days.
A set of overlapping opinions in the case collectively suggested that a majority of the justices are prepared to apply broad privacy principles to bring the Fourth Amendment's ban on unreasonable searches into the digital age, when law enforcement officials can gather extensive information without ever entering an individual's home or vehicle.
Walter Dellinger, a lawyer for the defendant in the case and a former acting U.S. solicitor general, said the decision was "a signal event in Fourth Amendment history."
"Law enforcement is now on notice," Dellinger said, "that almost any use of GPS electronic surveillance of a citizen's movement will be legally questionable unless a warrant is obtained in advance."
An overlapping array of justices were divided on the rationale for the decision, with the majority saying the problem was the placement of the device on private property.
But five justices also discussed their discomfort with the government's use of or access to various modern technologies, including video surveillance in public places, devices that allow motorists to signal for roadside assistance, location data from cellphone towers and records kept by online merchants.
The case centered on Antoine Jones, who was the owner of a Washington nightclub when the police came to suspect him of being part of a cocaine-selling operation. They placed a tracking device on his Jeep Grand Cherokee without a valid warrant, tracked his movements for a month and used the evidence they gathered to convict him of conspiring to sell cocaine. He was sentenced to life in prison.
The U.S. Court of Appeals for the District of Columbia Circuit overturned his conviction, saying the sheer amount of information that had been collected violated the Fourth Amendment, which bars unreasonable searches.
The Supreme Court affirmed that decision, but on a different ground.
"We hold 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, constitutes a 'search,' " Justice Antonin Scalia wrote for the majority.
Chief Justice John Roberts and Justices Anthony Kennedy, Clarence Thomas and Sonia Sotomayor joined the majority opinion.
In a concurrence for four justices, Justice Samuel Alito faulted the majority for trying to apply 18th century legal concepts to 21st century technologies. What should matter, he said, is the contemporary reasonable expectation of privacy. "The use of longer-term GPS monitoring in investigations of most offenses impinges on expectations of privacy," he wrote.
Justices Ruth Bader Ginsburg, Stephen Breyer and Elena Kagan joined the concurrence.