Analysis of the Wi-Fi signal allows you to monitor people who are on the other side

London. University College UCL. Engineers Carl Woodbridge and Kevin Chetty invented a device with which you can fix the movement behind a solid wall.

The device operation is based on the Doppler effect: when a wave is reflected from a moving object, its frequency changes. Wi-Fi signals sent by a router that operates at 2.4 or 5 GHz frequency are used as such waves. At the moment they are very common in many offices and buildings.

Thus, this device will, literally, allow you to look through walls, in a building where there is Wi-Fi radiation.

The device consists of two antennas. The first receives signals from base stations located nearby, the second tracks the reflected waves and measures their frequency.
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The software compares the data and determines the presence of moving objects in the Wi-Fi coverage area, plus the direction of their movement and speed of movement.

When approaching the router, the frequency of the reflected signal increases, with distance it decreases.

During test trials, the radar accurately determined the movement of people beyond a 30 centimeter brick wall. Since the device only receives signals, but does not send, it cannot be detected by conventional methods.

Use in military and espionage activities, special forces and everything connected with it. In a modified version of the device, the authors plan to increase its sensitivity so that it will be possible to capture the movements of the chest during breathing. You can also determine whether a person is sitting or standing behind a wall.
The radar fits easily in a briefcase, for its operation only a Wi-Fi router is needed, which will illuminate the scanned room with its beams.

The main advantage of similar devices from it: portability and difficulty in detecting.

True, the object of surveillance can be any person who has a Wi-Fi router in their home. In this regard, wallpaper that blocks the Wi-Fi signal becomes particularly relevant.

Source: here