Finding Life

The most critical job after a building collapses is searching for survivors
in the rubble. The tools available to locate people are varied, since living
humans give off many detectable signals: body heat, odor, noise, movement.
Cell phones can also be detected. 

New products, like those from Digital Angel, add an active component: this
company makes GPS-equipped watches that transmit position as well as
telemetry (like pulse and ambient temperature). The products were originally
created to locate and evaluate "wanderers," such as children or people
suffering from Alzheimer's (the senior product also can detect a fall).
Digital Angel is now developing a product for rescue workers who may become
trapped in buildings. 

http://www.digitalangel.net/products/senior.htm
http://www.wherifywireless.com/prod_watches.htm