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 sensor is an NTC with a resistance of the order of 2k. The SCR can be from the TIC...
The load current can be adjusted up to about 1 A. The transistor can be TIP32 or TIP42. The...
This oscillator with common general-purpose transistors appeared in Radio Electronics magazine in...