This is the receiver from the previous alarm system. The circuit is from Radio Electronics, April 1989, and has an LDR as the sensor. Optical devices should be used to improve performance.
The circuit shown is from an old European publication. In it we have the way to activate a relay...
We found this circuit in a European publication from the 1990s. Transistors are still common types...
This circuit was found in an American documentation and can be added to common amplifiers of any...