This simple circuit, found in American documentation, uses only one relay that locks when any of the sensors is activated. To reset, simply turn off the power for a moment.
This 555 IC circuit was found in June 1984 Radio Electronics magazine. This circuit detects a...
We found this circuit in a 1976 publication for radio amateurs. It was originally intended for use in...
The integrated circuit used in this small transmitter is not very common today. The coil has its...