The government's use of controversial stingray devices just got a little more stringent and transparent—at least at the federal level.

On Thursday the Justice Department announced a new and long-overdue policy requiring the FBI and other federal agents to obtain a search warrant before using stingrays—devices that simulate a cell phone tower in order to track the location of mobile phone users.

The new policy forces prosecutors and investigators not only to obtain a warrant but also to disclose to judges that the specific technology they plan to use is a stingray, as opposed to another surveillance tool.

Law enforcement agencies throughout the US have been criticized for using the powerful technology without a warrant, and for deceiving judges about the nature of the technology they were using to track suspects—telling courts that they planned to use a pen-register or trap-and-trace device to obtain location data on a suspect, rather than a stingray, which is much more invasive. The Justice Department, however, appeared to deny that prosecutors and federal investigators have been using the devices without a warrant in its announcement today.

"While the department has, in the past, obtained appropriate legal authorizations to use cell-site simulators, law enforcement agents must now obtain a search warrant supported by probable cause before using a cell-site simulator."

Stingrays are mobile surveillance systems the size of a small briefcase that impersonate a legitimate cell phone tower in order to trick mobile phones and other mobile devices in their vicinity into connecting to them and revealing their unique ID and location. Stingrays emit a signal that is stronger than the signal of other cell towers in the vicinity in order to force mobile phones and other devices to establish a connection with them and reveal their unique ID. Stingrays can then determine the direction from which the phone connected with them, data that can be used to track the movement of the phone as it continuously connects to the fake tower.

The policy is something civil liberties groups have been seeking for years, but it does not cover local and regional law enforcement, who also use stingrays to track suspects.

Civil liberties groups have long asserted that stingrays are too invasive because they can sweep up data about every phone in their vicinity, not just targeted phones, and can interfere with their calls.

Justice Department and local law enforcement agencies have refused to confirm that the devices can interrupt cell service for anyone in their vicinity. But earlier this year, this issue was confirmed in a warrant application requesting approval to use a stingray, in which FBI Special Agent Michael A. Scimeca disclosed the disruptive capability of the devices to a judge.

“Because of the way, the Mobile Equipment sometimes operates,” Scimeca wrote in his application, “its use has the potential to intermittently disrupt cellular service to a small fraction of Sprint’s wireless customers within its immediate vicinity. Any potential service disruption will be brief and minimized by reasonably limiting the scope and duration of the use of the Mobile Equipment."

The new Justice Department policy around the use of stingrays allows for exigent circumstances or exceptional circumstances, whereby law enforcement agents can use the devices without a search warrant in emergency situations when obtaining a warrant is not practical. But the DoJ will be required to track and report the number of times the technology is deployed under these exceptions.

Equally important to the new notification and warrant requirement, the policy also now requires federal law enforcement agents to delete all data the stingray collects "as soon as" it has located the device it's tracking. This is particularly important in light of the fact that the devices collect data on all mobile devices in their vicinity, not just the mobile phone law enforcers are tracking. The Justice Department also plans to implement an agency-level auditing program to sure that data is being deleted according to the new policy.

The Justice Department addressed another issue around the use of the devices by asserting that the cell-site simulators "may not be used to collect the contents of any communication in the course of criminal investigations. This means data contained on the phone itself, such as emails, texts, contact lists and images, may not be collected using this technology." Although law enforcement agencies have long insisted that the devices do not collect the contents of communication, questions have remained about whether they are capable of intercepting such data and, if so, whether they can be abused for this purpose. The new policy makes it clear that the devices should not be configured for intercepting data.

Although the new policy is something civil liberties groups have been seeking for years, the new federal policy does not cover local and regional law enforcement, who also use stingrays to track suspects. Also, although the policy means that the Justice Department will now be more carefully tracking the number of times federal agents use stingrays, there is currently no law requiring the agency provide an annual report to Congress about their use—which the agency is currently required to do with regard to wiretapping and the use of national security letters.