mi writes At least 50 U.S. law enforcement agencies have secretly equipped their officers with radar devices that allow them to effectively peer through the walls of houses to see whether anyone is inside. The device the Marshals Service and others are using, known as the Range-R, looks like a sophisticated stud-finder. Its display shows whether it has detected movement on the other side of a wall and, if so, how far away it is — but it does not show a picture of what's happening inside. The Range-R's maker, L-3 Communications, estimates it has sold about 200 devices to 50 law enforcement agencies at a cost of about $6,000 each. Other radar devices have far more advanced capabilities, including three-dimensional displays of where people are located inside a building, according to marketing materials from their manufacturers. One is capable of being mounted on a drone. And the Justice Department has funded research to develop systems that can map the interiors of buildings and locate the people within them.