How the government can still track your vehicle without GPS

The U.S. Supreme Court unanimously ruled today that law enforcement agencies can't track a vehicle by planting a GPS device without a warrant. It's a win for civil liberties, but the court punted on the bigger question of how far police can go to follow the increasingly vivid electronic trail left by driving.

In the case decided today, federal agents planted a GPS tracker to a Jeep Grand Cherokee owned by a suspect in a drug case, following his movements for 28 days and generating enough data to fill 2,000 pages. The suspect, Antoine Jones, was later convicted of drug trafficking and sentenced to life in prison.

An appeals court sided with Jones and threw out the conviction, finding the government had violated the Fourth Amendment's bar of unreasonable search and seizure because it had not asked for a warrant before planting the GPS. The Supreme Court agreed, saying the government violated Jones' constitutional rights when it physically attached the GPS unit to his Jeep.

But the court's ruling focused on how the government attached the unit, and struggled with whether the government could have legally followed Jones if it never touched his vehicle, and only used electronics to track him. "It may be that achieving the same result through electronic means, without an accompanying trespass, is an unconstitutional invasion of privacy," Justice Anthony Scalia wrote in the majority opinion, "but the present case does not require us to answer that question."