The U.S. Department of Homeland Security has customized its Predator drones, originally built for overseas military operations, to carry out at-home surveillance tasks that have civil libertarians worried: identifying civilians carrying guns and tracking their cell phones, government documents show.

The documents provide more details about the surveillance capabilities of the department's unmanned Predator B drones, which are primarily used to patrol the United States' northern and southern borders but have been pressed into service on behalf of a growing number of law enforcement agencies including the FBI, the Secret Service, the Texas Rangers, and local police.