A motion tracking system makes use of a number antennas to transmit and receive radio frequency signals that are reflected from objects (e.g., people) in the environment of the system, which may include one or more rooms of a building, the interior of a vehicle, etc., and may be partitioned, for example, walls or cloth sheets. In general, the objects in the environment include both fixed objects, such as chairs, walls, etc., as well as moving objects, such as but not limited to people. The system can track people, who may be moving around a room, or may be relatively stationary, for instance, sitting in a chair of lying in bed, but may nevertheless exhibit breathing motion that may be detected. The system may detect body or limb gestures made by the people in the environment, and detect physical activity including detection of falls.