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.
The two previous circuits show the INA185 a current sensing amplifier in basic applications. This...
This metronome configuration with the 555, quite common was found in a 90s Hands On Electronics. The...
This bidirectional circuit was found in an American documentation from the 80's. The LEDs are...