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.
I mentioned this in a another reply, but you just need a microwave oven basically :)
Super now I just need to find one of these in portable form factor. And a good battery.