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.
The maximum frequency of the oscillator shown in the figure is around 3 MHz. The trimmer adjusts the...
This circuit was obtained in a 1977 Radio Handbook. The transistor is from the era and the coils...
August 2017 - STMicroelectronics' BlueCoin development environment is available at Mouser...