We found this alarm in an English publication from 1978. Although the original power supply is 3 V, the 2 V drop in the SCR practically renders the buzzer (Bell) inoperative. Thus, we suggest feeding with 6 V and using a 3 V buzzer with oscillator or powering with 12 V and using a relay. The transistors can be the BC548 and the SCR the TIC106.
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