The Cinside radars transmits electromagnetic energy (radio waves) of a certain frequency, which is reflected in all surfaces it hits. The energy also penetrates all kind of materials, except homogenous metal plates. This allows for some portion of the transmitted wave to travel through the first wall and after a series of reflections and penetrations eventually return to the sensor.
What enables the discrimination between static and moving objects is called the Doppler Effect. When a wave is reflected off a static object the frequency remains the same before as after reflection. However, for moving objects the frequency of the wave changes when reflected. By comparing the frequency of the transmitted and the received wave our systems determine if there is movement behind the examined wall.