Halloween circuits

[BrownOut]

I use PIR detectors for all kinds of stuff. I can't imagine why someone would use anything else.

 

[giftiger_wunsch]

IR receiver modules are also pretty cheap and easy to use. You can probable salvage one, most things use a remote these days. Plenty of examples of how to build a 38khz transmitter using a 555 timer. The output of the module goes low, while receiving, so it will go high, and trigger what ever you want, when the path is blocked.

I can personally vouch for how easy this is to build as I'm an electronics noob and this is about the second thing I ever created