Since you're on vacation, like me, you've probably got some time on your hands. Here's a nice project to do with the kids. I'm sure you've got a circuit board and a LM741 microchip lying around since ...

It takes input from the laser detection circuit, triggers the buzzer, as well as arms and disarms the entire alarm system. An LS7222 digital lock handles the passcode verification side of things ...

[Gordon] sent us a tip about this simple laser ... security unit. That build did a lot to provide functionality, such as a system to disarm the trip wire, and a robust light detection circuit.