 -- In a major policy shift, the Justice Department announced today that the FBI, DEA and U.S. Marshals Service will now have to obtain a warrant before using a cellphone scanning device to track down wanted criminals. Until today, those law enforcement agencies have been able to use those devices -- commonly known as Stingrays -- virtually at will.

DOJ officials confirmed today that Stingrays are widely used by federal, state and local law enforcement in criminal investigations: the U.S. Marshals Service has a fleet of planes stationed at airports around the country equipped with Stingrays to hunt for federal fugitives. The FBI says it has used the technology in high-profile kidnapping cases, and the DEA often employs it to run down drug dealers. Baltimore police have acknowledged using Stingray technology on more than 4,000 cases since 2007.

The Stingray technology can locate a specific suspect by scanning thousands of phones to pinpoint the suspect’s phone signal. But the cellphones and locations of thousands of innocent people can be ‘pinged’ by a Stingray while it is searching for a suspect’s phone in the sea of digital signals. Some privacy advocates have raised concerns, and charge that the technology violates the rights of cellphone users whose location is swept up in the search for a criminal.

Federal and local law enforcement officials traditionally have been reluctant to talk about how the technology works, and when and how they employ it. Deputy Attorney General Sally Quillian Yates said today law enforcement officials have not wanted to disclose much about Stingrays, because they didn’t want to “give the bad guys a road map on how to defeat it.”

In announcing the policy change, Yates said the Stingray technology has been “instrumental in aiding law enforcement in a broad array of investigations, including kidnapping, fugitive investigations and complicated narcotics cases.” But she conceded that there were no consistent guidelines in federal law enforcement for the use of Stingrays. She could not even say how many times federal agents have used Stingrays in the recent past.

“The cell simulators do not collect any content,” Yates pointed out, but “this new policy ensures our protocols for this technology are consistent, well-managed and respectful of individuals’ privacy and civil liberties.”

In addition to the requirement to obtain a search warrant, the new policy:

Bans using the technology to collect the content of any communication in the course of criminal investigations. E-mails, texts, contact lists and images held on the phone itself are out-of-bounds.

Requires that when the technology is use to located a known cellphone, all other unrelated data collected must be deleted as soon as the targeted device is located

Establishes new management controls that will track and report the number of times the technology

is employed

Provides limited, emergency exceptions to the requirement of obtaining a warrant, such as in the case

of a child kidnapping

Today’s policy change does not apply to state and local police, or Department of Homeland Security agencies like the Secret Service, but Yates conceded that the new DOJ rules would probably have a “trickle-down effect” and eventually impact law enforcement’s use of Stingray’s nationwide.