"This is the first case considering when the government can track the movements of your cell phone, and the answer couldn't be more important," said EFF Staff Attorney Kevin Bankston. "Allowing the government to turn anyone's cell phone into a tracking device without probable cause will enable a surveillance society that would make Big Brother jealous."

Last month, the court denied a Justice Department request to monitor a cell phone's location. The ruling revealed that the DOJ has routinely been securing court orders for real-time cell phone tracking without probable cause and without any law authorizing the surveillance.

Many cell phone users aren't aware that their phones can be used to track their location in real-time, even when they aren't using them. EFF filed a friend-of-the-court brief on Friday to oppose a DOJ motion asking the court to reconsider its pro-privacy decision. EFF argues that the Fourth Amendment requires a search warrant for such invasive surveillance, issued under the same strict standards as warrants that authorize phone and Internet wiretaps.

The government has tried to justify this gross expansion of its authority by combining two surveillance statutes, neither of which authorize cell phone tracking on their own. As EFF explains in its brief, there is no support anywhere for this argument -- not in the statutes' language, nor in legislative history, case law, or academic commentary. Indeed, it contradicts the government's own electronic evidence manual. "It's as if the government wants the court to believe that zero plus zero somehow equals one," said Bankston.

EFF's brief marks the first time the DOJ has had to face lawyers presenting an opposing argument on this issue. "Secrecy breeds abuse," said EFF Staff Attorney Kurt Opsahl. "Before this court had the courage to stand up to the government, the hearings were hidden from the public and the judge only saw the government's point of view; this led to secret tracking orders -- without basis in law -- that threaten our fundamental liberties."

The DOJ is expected to appeal to the district court if Magistrate Judge Orenstein denies its motion to reconsider. The court has not said when it intends to rule.

You can read the full text of the EFF brief