The feds and law enforcement agencies across the country have been using devices called StingRays to track down mobile phone users. More importantly, not only have they not gotten warrants for their use, they’ve been concealing this information from the courts (and obviously therefore from defendants and their counsel).  
In May, the Department of Justice announced it was mulling over some possible changes to make StingRay use more transparent. They’ve finally pulled the trigger this week. Federal agents will have to obtain a search warrant (and therefore make its use a matter of public record) in order to use StingRays to track location data. From Wired:
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. …
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.
The new policy states that these devices also may not be used to collect the contents of any communications or any data saved on smartphones and requires the deletion of any extraneous data gathered by the devices daily.
While this new policy covers only federal law enforcement, it’s also been established that the FBI was partly responsible for pushing municipal law enforcement agencies to keep use of StingRay devices a secret, complete with non-disclosure agreements. Will those go away now, too?
Below, ReasonTV on the secretive use of StingRay surveillance by law enforcement: