hypnosec writes "Researchers at University College of London have applied principles of radar used in defense and designed a detector using home based Wi-Fi routers to spy on people across walls. Using the principles behind the Doppler effect ... Karl Woodbridge and Kevin Chetty, at University College London, have built a prototype unit that uses Wi-Fi signals and recognizes frequency changes to detect moving objects. The size of the prototype unit is more or less the size of a suitcase. The unit contains a radio receiver comprising of two antennas and a signal-processing unit. The duo carried out test runs and ... they managed to determine a person's location, speed, and direction (even through a one foot thick brick wall). The device could be used to spot intruders, monitor children or the elderly, and could even be used in military applications."
All theoretical chemistry is really physics; and all theoretical chemists
-- Richard P. Feynman