The sensor is placed in the bilge at a level where there is normally no water.
If water unexpectedly comes up to alarm level, the buzzer (sold separately) will warn you, so you can take action.
This is a good investment for safety on board.
For buzzer order #BZ-1
This product can expose you to chemicals which are known to the State of California to cause cancer, birth defects or other reproductive harm.
www.P65Warnings.ca.gov