detector

noun4

1. •
   A device capable of registering a specific substance or physical phenomenon, and that optionally sounds an alarm or triggers a warning.

   • Smoke detectors are mandatory in public buildings.
2. •
   An indicator showing the depth of the water in a boiler.
3. •
   A galvanometer, usually portable, for indicating the direction of a current.
4. •
   A device measuring radiation or electromagnetic waves.