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.
It has to be trained on the disturbances in the EM field that people create so no, an empty office wouldn’t train it.
But… if the router collects the data… it is just a matter of time. The room will stay constant. People will change. And there you have the fundamental information to infer ID