LA Times 
January 23, 2012
The Supreme Court on Monday put the brakes on the government’s use of high-tech monitoring devices to track motorists, ruling unanimously  that police and the FBI violated the 4th Amendment by attaching a GPS device to a Jeep owned by a drug suspect.
The justices all agreed that the government needs a search warrant from a judge before it seeks to track a suspect by secretly installing a device on his car.
They were divided, however, as to what level of tracking would require a search warrant. Justice Antonin Scalia, speaking for a five-member majority, said the police erred because they attached the tiny device to the vehicle. He said the 4th Amendment was intended to protect against government searches on private property.
“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,'” Scalia said. “The government physically occupied private property for the purpose of obtaining information,” he said.