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.
Found in 90's Electronic Engineering, this circuit produces a pulse with a delay that depends on R3...
This circuit was found in the December 1984 issue of Radio Electronics magazine. The circuit has a...
Found in 90s Radio Electronics, this circuit is intended for amplifying analog video signals....