A sound detector.
Sound detector
A cobra detector is a radar detector. Radar detectors work the same way a radio receiver does. The radar detector looks for frequencies that a radar gun uses.
Then it wouldn't be a smoke detector, but there are fire alarms that are triggered by temperature.
metal detector
Sure, but what you would have to do would be to put the switch in the TEST circuit of the detector.
machudao
no
Sonar detector.
boh
It is a motion detector that detects motion using sound waves
Sonic detectors pick up sound waves and motions When things move, they often create changes in surrounding Read more: How Does a Sonic Motion Detector Work? | eHow.com http://www.ehow.com/how-does_4564490_sonic-motion-detector-work.html#ixzz1R9OT0diL not all written by me