Unmanned drones are carrying out an expanding menu of tasks, from shooting missiles into terrorist camps to delivering books for Amazon.

But robots and drones are also proving very useful to U.S. Customs and Border Protection, and other law enforcement agencies are taking note. In fact, a recent FOIA request revealed an increasing demand by law enforcement agencies to borrow drones from the Border Patrol, which has the largest fleet outside the Defense Department.

For example, Customs and Border Protection flew almost 700 surveillance missions for other agencies from 2010 to 2012.

U.S. Customs and Border Protection use the drones with high-resolution cameras, radar and night vision equipment for surveillance to spot individuals and vehicles crossing the borders. They are also using robots to crawl through sewer tunnels that criss-cross the border and are sometimes used  to smuggle contraband. Law enforcement uses drones for spotting drug grows and labs, searching for missing persons and mapping disaster relief, among others.

Congress has ordered the FAA to allow more drone traffic in the coming years, according to the Washington Post, but there are increasing worries that growing numbers of drones flitting about with high-tech surveillance gear pose a significant new privacy challenge, especially as they proliferate and are employed for a larger variety of tasks. The issue was discussed by the Senate Commerce, Science and Transportation Committee this week, and in the wake of the NSA surveillance issue, drones are likely to persist in privacy debates for some time to come.