The opinion is available here.
Issue: Whether the Constitution allows police to put a tracking device on a car without either a warrant or the owner's permission; and whether the Constitution is violated when police use the tracking device to keep track of the car's whereabouts.
Supreme Court limits police use of GPS to track suspects - Chicago Tribune
The Supreme Court for the first time ruled on Monday that police attachment of a GPS device to monitor a suspect's vehicle was a search protected by constitutional privacy rights, a test case involving new surveillance technology.The high court's ruling was a defeat for the Obama administration, which defended the use of global positioning system devices without a warrant and without a person's knowledge as a legal way to monitor a vehicle on public streets.
The justices upheld a precedent-setting ruling by an appeals court that the police must first obtain a warrant to use a GPS device for an extended period of time to covertly follow a suspect.The high court unanimously held the government's placement of the GPS device to a vehicle and using the device to monitor the vehicle's movement was covered by U.S. constitutional protections against unreasonable searches and seizures of evidence.