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.
Wifi tracking uses measurements of the interference caused when objects pass between connected devices and a router. For your neighbors to track your movements their router would have to be connected to a device in your house, or maybe in the other neighbor’s house on the far side of your house, so when you walk around it interferes with that signal.