The Supreme Court is considering whether police use of GPS devices to track criminal suspects requires a judge's advance approval.
The case being argued Tuesday could have implications for other high-tech surveillance techniques in the digital age.
The Obama administration is appealing a ruling that threw out the drug conspiracy conviction of Antoine Jones of Washington because FBI agents and local police installed a GPS device on Jones' car and collected travel information without a search warrant.
The government argues that people have no expectation of privacy concerning their travel on public streets.
The GPS device helped authorities link Jones to a suburban house used to stash money and drugs. He was convicted and sentenced to life in prison before the federal appeals court in Washington overturned the conviction.
The appellate judges said the authorities should have had a warrant and pointed to the length of the surveillance _ a month _ as a factor in their decision.
An unusual array of interest groups backs Jones, including the Gun Owners of America, the Council on American-Islamic Relations, the American Civil Liberties Union and an association of truck drivers. The groups say GPS technology is much more powerful than the beeper technology police once employed in surveillance.
But the Justice Department says the GPS device is no different from a beeper authorities used, with the high court's blessing in 1983, to help track a suspect to his drug lab. The court said then that people on public roads have no reasonable expectation of privacy.
The Justice Department said GPS devices are especially useful in early stages of an investigation, when they can eliminate the use of time-consuming stakeouts as officers seek to gather evidence.
Other appeals courts have ruled that search warrants aren't necessary for GPS tracking.
The justices will be considering two related issues, whether a warrant is needed before installing the device or using the GPS technology to track a vehicle.