US v. Katzin
Together with the ACLU and the National Association of Criminal Defense Lawyers, EFF filed an amicus brief arguing police needed to obtain a search warrant in order to monitor a car's location with a GPS device.
FBI agents installed a GPS device on a minivan without a search warrant to track the movements of three brothers suspected of committing a string of robberies. The trial court found the collection of the GPS evidence violated the Fourth Amendment and suppressed it. The government appealed to the Third Circuit Court of Appeals, arguing the agents didn't need to get a warrant to gather the GPS evidence because the Supreme Court's decision in United States v. Jones held only that a warrant is required to install a GPS device, but didn't reach the question of whether a warrant is required to monitor a person's movements using that device.
In an important and lengthy decision, a three judge panel of the Third Circuit rejected the government's argument and instead ruled the police needed to obtain a warrant supported by probable cause to both install and use the GPS device. It also rejected the government's argument that the officers weren't required to get a warrant, since they installed the device before Jones was decided, and so were relying in good faith on the law as it existed at that time. Unfortunately, the Third Circuit sitting en banc reversed the panel's decision that officers could rely in good faith on earlier cases involving beeper technologies to install a GPS device, and reversed the panel's decision suppressing evidence.