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.
The wavelength of a 5 Ghz wifi signal (the highest frequency in common use for wifi) is a little under 6 cm. So as a crude measure, it’s not going to resolve spatial features much smaller than that with much reliability.