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 is from an Electronics World of 1968. The transistors are of the time and the power...
This circuit was found in a 1967 Raytheon optoelectronics manual. The circuit uses tubes. | Clique...
This interesting circuit shows on a display the sequence of numbers corresponding to a decimal from 1...