The sensor of this circuit found in Popular Electronics can be formed by a piece of fabric between two bare wire screens. When wet, the fabric will pass the current between the screens, triggering the alarm.
This circuit, found in an American publication from the 1970s, produces an audible tone in a...
This circuit was found in a 2006 publication. It can serve as the basis for a microcontrolled...
By adding a transistor to the output and some polarization features we can obtain a higher output...