The Justice Department on Friday will publicly defend a little-known law-enforcement practice that allows federal prosecutors to obtain the collection of cell-phone “tracking” records that identify the physical locations where the phones have been, reports Newsweek’s Michael Isikoff:

It may come as a surprise to most of the owners of the country’s 277 million cell phones, but their cell-phone company retains records of where their device has been at all times—either because the phones have tiny GPS devices embedded inside or because each phone call is routed through towers that can be used to pinpoint the phone’s location to within areas as small as a few hundred feet.

“Most people don’t understand they are carrying a tracking device in their pockets,” says Kevin Bankston, a lawyer with the Electronic Frontier Foundation, a privacy group that has been trying to monitor the Justice Department’s practice.

According to the Newsweek article:

A panel of three federal judges in Philadelphia on Friday is due to hear oral arguments in a landmark case in which Bankston’s group and the ACLU are contending that the Justice Department’s cell-phone tracking practice raises profound “privacy” issues under the Fourth Amendment to the Constitution. The groups contend the Justice Department should be required to first obtain the equivalent of search warrants from federal judges in which they would have to establish “probable cause” that the records will actually yield evidence of a federal crime.

Read more from Newsweek: Can the FBI Secretly Track Your Cell Phone? – Declassified Blog.