This simple optical alarm circuit was found in the 1991 Electronics Experimenter Handbook. The circuit uses a lamp as the emitter but can use LEDs.
This circuit was found in documentation from the 1980s. The integrated circuit used is uncommon today...
This circuit activates a relay that has a lamp as a load. The circuit is from a Radio Electronics from...
This circuit was found in a 90s Popular Electronics. The circuit uses several relays in order to...