The invisible and the non-existent look very much alike

The US Department of Homeland Security is developing a system designed to detect "hostile thoughts" in people walking through border posts, airports and public places. The DHS says recent tests prove it works.

'Pre-crime' detector shows promise

A 2005 DARPA report... proposes to "image through multiple walls and even penetrate whole buildings using distributed sensors on or around buildings," with UAVs assisting ground forces. A 2007 Army Research Lab study explores the ability of ground sensors, working with UAVs, to capture "images from different angles," thereby providing "intelligence on the configuration, content, and human presence inside enclosed areas (buildings)."

Nowhere To Hide - Killer drones that can see through walls