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.
We found this circuit in an American 1980s documentation. The circuit uses a piezoelectric transducer...
A ring and pendulum of stripped wires form the sensor for this alarm. Once triggered, to reset, you...
Other operational amplifiers in the series, such as the MC34072, MC34074, MC35071, MC35072,...