Can your car be tracked without a warrant?

PHILADELPHIA A federal appeals court is being asked to decide if the government must obtain a warrant before placing a GPS tracker on a suspect's car.

The case before the 3rd U.S. Circuit Court of Appeals in Philadelphia involves three brothers suspected of robbing pharmacies. A GPS device led to their arrests in 2010.

Lawyers representing the trio told a three-judge panel Tuesday that warrantless tracking violates the constitutional guarantee against unreasonable searches.

But a federal prosecutor contends that authorities followed relevant legal precedents in attaching the tracker without a warrant. He says authorities had probable cause to suspect illegal activity.

A lower court previously ruled in favor of the brothers. The Justice Department appealed based on a recent Supreme Court ruling. It's unclear when the appeals court will rule.

Associate Justice Antonin Scalia said during the January Supreme Court ruling that the government's installation of a GPS device, and its use to monitor the vehicle's movements, constitutes a search, meaning that a warrant is required.

CBS News legal analyst Andrew Cohen said the decision was a victory for civil libertarians and a defeat for law enforcement officials who had argued that putting a GPS device on a car wasn't exactly a search under the Fourth Amendment.

"Perhaps the biggest surprise is that the justices were unanimous," said Cohen. "All of the Justices agreed that placing a GPS monitor on a suspect's car triggered the protections of the Fourth Amendment's protections against unreasonable searches and seizures. But the Court didn't say whether the search here was reasonable or not."

That last point of contention is the focus of the appeals court ruling.