Most forms of radar are blocked by walls and other solid objects, David Hambling explains (in Swarm Troopers), but there are also through-the-wall “life detection” radars:
These use ultra-wideband radio waves, which can go through solid walls as easily as air. Life detection radar works on the Doppler principle and only detects movement, in particular the movements associated with human life — breathing and heartbeats. First responders use portable units in rescue operations to detect if there are people alive in a building. It is imprecise but will give the number and approximate location of any people inside. The technology is also used by the military and police.
The principle applies whatever the source of the wall-penetrating radio waves in question.