Scientists in Germany have demonstrated a startling new form of surveillance: identifying people using nothing more than ordinary WiFi signals. By analyzing how radio waves bounce around a room, researchers can effectively “see” and recognize individuals — even if they are not carrying a device and even if their phone is turned off.
Funnily enough, indoors, this would probably make you more visible as the only area with no reflections. Stealth works outdoors because the sky does not have a radar return.