trip meter

[chaosfourever]

I wanna make a IR trip meter where when the beam is broken like an alarm woulf go off or turn a light on or something. any suggestions?

 

[turtlecannon]

http://www.metacafe.com/watch/1133002/protect_your_home_with_laserbeams might be a good place to start. I built one of these but I modified the circuit slightly so it actually stays on after getting tripped.