The olympic WiFi-Police
Somehow related: Wissenschaftler haben einen Radar entwickelt, der mit WiFi-Signalen arbeitet. PopSci: Seeing Through Walls With a Wireless Router.
Wi-Fi radio signals are found in 61 percent of homes in the U.S. and 25 percent worldwide, so Karl Woodbridge and Kevin Chetty, researchers at University College London, designed their detector to use these ubiquitous signals. When a radio wave reflects off a moving object, its frequency changes—a phenomenon called the Doppler effect. Their radar prototype identifies frequency changes to detect moving objects.