Thirty-four ACLU affiliates in 31 states filed 379 public records requests in 31 states around the nation on Wednesday, demanding information about how law enforcement agencies use mobile-phone location information.

Claiming to "lift the veil on this secrecy," the American Civil Liberties Union said it wants data about when the location information is sought and under what standards.

"While we believe that law enforcement should always be required to obtain a warrant based on probable cause to access cell-phone location information, the scary truth is that they don't always obtain said warrant, and courts don't always insist that they do," according to a statement from the group.

The ACLU claims that mobile devices continuously send out signals searching for the nearest cell tower to ensure calls go through, and cellular providers can estimate a user's location with ever-improving accuracy based on their proximity to nearby towers. Each cellular provider determines the amount of time they store this information, and in how much detailm according to the ACLU.

The data can be used by law enforcement agencies to track people's movements.

FBI agents investigating a series of bank robberies collected the records of every cell phone that was near each bank when it was robbed in 2008, reports CNET .

The public-records requests seek information about whether law enforcement agents demonstrate probable cause and obtain a warrant to access cell phone location data; statistics on how frequently law enforcement agencies obtain cell phone location data; how much money law enforcement agencies spend tracking cell phones; and other policies and procedures used for acquiring location data.

The ACLU's national chapter posted an interactive map that allows users to view the requests from each state.