This interesting alarm was obtained in an American technical documentation from the 1970s. We can use both NA and NC sensors. The circuit can be easily assembled with BC548 transistors and a TIC106 SCR. The diode can be 1N4148 or even 1N4004. The circuit is characterized by extremely low consumption in the standby condition. A suggestion is to use a 6 V supply with a 5 V relay or a 12 V supply with a 12 V relay. The sensors can have unlimited quantity and long connection wires. Do not use a power source without a transformer to power this circuit.
