Concept art (via Kevin Hard & Teknisk Ukeblad)
Those looking to commit crimes by hiding out where no one can see them, better think again. WiFi signals bathe other everything, including criminal activity. Law enforcement may employ a high-tech toy in the form of a Passive Bistatic WiFi Radar that can see through walls. The bad guys can't hide. (This is similar to the "Doppler" radar Batman used in the film "The Dark Knight.")
Signal process, how it can see through walls (via Locating a moving target in a high clutter environment)
Developed by researchers Karl Woodbridge and Kevin Chetty (from University College London), the design works similar to Doppler radar, which tracks the velocity and location of an object using radio signals (the frequency changes when it hits a target). However, their detection system uses WiFi-based signals to track an individual’s location, speed, and direction through high-clutter indoor environments, as opposed to weather or aircraft. The pair’s system was designed using a 2.4-GHz passive multi-static receiver (the size of a suitcase) that is equipped with two antennae with one used to monitor base WiFi signals in a given hotspot and the other to monitor reflected WiFi signals that have changed frequencies. The receiver takes the WiFi data and sends it to a computer where it analyzes the signal discrepancies and pinpoints the targets location. For example; the device can take a base-line reading (usually 2.4 or 5GHz) from your router in your residence. When you move closer or further from the router its signal changes to either a higher frequency or lower depending on your distance. By comparing the base-line to the altered signal, the system can pin-point your location (within a few feet) in real-time.
The researcher’s state that with a little more development they can refine their system using what’s known as a ‘Clean algorithm’ (de-convolutes an image in radio astronomy based off of a series of point sources). This would clean up any static interference and make their system sensitive enough to detect a person’s rib-cage movement while breathing!