Enfin en théorie ... mais l'idée n'est pas bête, et peut certainement être appliquée à d'autres ondes.
Source:
Wi-Spy Click here to see this amazing image even larger. Kevin Hand
popsci.com
L'explication en anglais des chiffres 1 à 5
1. MOVING SUBJECT
When Wi-Fi radio waves bounce off a moving object, their frequency changes. If, for example, a person is moving toward the Wi-Fi source, the reflected waves’ frequency increases. If a person is moving away from the source, the frequency decreases.
2. REGULAR OL' ROUTER
A Wi-Fi Internet router already in the room fills the area with radio waves of a specific frequency, usually 2.4 or 5 gigahertz.
3. BASELINE SIGNAL
One antenna of the radar system tracks the baseline radio signal in the room.
4. SHIFTED SIGNAL
A second antenna detects radio waves that have reflected off of moving objects, which changes their frequency.
5. PERP, SPOTTED
By comparing the two antennas’ signals, the computer calculates the object’s location to within a few feet as well as its speed and direction.