We found this circuit in the September 1971 issue of Radio Electronics magazine. The sensor is an LDR and R1 adjusts the sensitivity. A relay with the appropriate voltage can be used instead of a buzzer.
In the original publication of the 90s a 556 consisting of a double 555 is suggested. The circuit...
This circuit was found in a 1966 EEE. The circuit uses transistors from the time but can be made...
This circuit can be used in alarms by activating a relay or a current load that depends on the...