The fight against cell tower simulators, commonly known as Stingrays, just scored a major victory. Today the Justice Department issued a new policy for the simulators, which requires a search warrant before any such device can be deployed, effective immediately. The legal status of the cell-site simulators is still uncertain, and the new policy won't have the force of law, but it's still expected to radically change the way federal law enforcement deploys the devices.

There are still some exception to the warrant requirement, but they're expected to be tracked and monitored significantly more rigorously than in the past. The relevant section of the new policy reads:

The use of cell-site simulators is permitted only as authorized by law and policy. While the Department has, in the past, appropriately obtained authorization to use a cell-site simulator by seeking an order pursuant to the Pen Register Statute, as a matter of policy, law enforcement agencies must now obtain a search warrant supported by probable cause and issued pursuant to Rule 41 of the Federal Rules of Criminal Procedure (or the applicable state equivalent), except as provided below.Specific exceptions follow for exigent circumstances as named in the Fourth Amendment, as well as circumstances where the pen register statute is more relevant than the traditional warrant requirement. Any applications granted under these exceptions are to be tracked and reported by the department components.

Taken together, the policy represents a significant break in how cell simulators are used — a break that groups like the American Civil Liberties Union have been advocating for years. The simulators work by mimicking the signals of a conventional 2G cell tower, allowing it to both locate and potentially pull data from the connecting device. Notably, the system is incompatible with more advanced networks like 3G and LTE, which authenticate towers before connecting.

Commenting on the rule, the ACLU expressed both optimism and concern. "After decades of secrecy in which the government hid this surveillance technology from courts, defense lawyers, and the American public, we are happy to see that the Justice Department is now willing to openly discuss its policies," said staff attorney Nathan Freed Wessler in a post. "However, this policy does not adequately address all concerns. Disturbingly, the policy does not apply to other federal agencies or the many state and local police departments that have received federal funds to purchase these devices."

5:01PM ET: Updated to include ACLU statement.