We found this circuit in the 1964 RCA transistors manual. The sensor may be a common LDR and the transistor BC558. The relay has an operating voltage according to the power supply.
This siren configuration found in a documentation from the 1980s can also be seen in many of our...
This alarm is either activated or triggered after a certain amount of time, giving the owner time...
This timer circuit is based on an integrated circuit configured as stable and a 14-stage 4020...