After fifteen years of effort, the U.S. Army and Navy have created robotic sentries to patrol indoors and outdoors. Called MDARS (Mobile Detection Assessment Response System), it comes in two different versions. The indoor MDARS runs off batteries and contains a huge number of sensors to enable it to navigate. These include twenty electrostatic and piezoelectric sonars (both narrow- and wide-beam), a monochrome video camera, an acoustical microphone, a scanning microwave and PIR motion sensors and optical beacon sensing modules, an ultraviolet flame sensor; a gas detector, laser retroreflective proximity sensors and a scanning laser rangefinder. The outdoor version (MDARS-E)...