Replacement Motion Sensor

For Halloween, every year I make compressed air "widgets" that leave a photocell regular (replacement of a light outside) motion detector. It worked very well, but it was difficult to get exactly what I wanted, not to mention he was going every time she passed a sheet. I thought of using those that have garage doors, but the only problem is she must be brought together by a thread that runs through the path concreate, this would have some problems. I was also thinking of a new called "electronic sensor field disturbance" but no one sells these (i do not want to build one) and I have no idea if it will even work. Any help would be greatly appriectiated thank you!

Look into the type of equipment alarm input that stores etc. use.Infrared light source, I believe, that shines a beam is broken reflector.When it trips.This way you have only one wire to the source .

I tinker with stuff on Halloween too.
The simpler the better in this case.
Probably one of the best things you can find a limit switch style mustache.
It works like a hair cats of course, and if it is bent in any direction it will close the contacts and scare the candy a little elf.
You can find a way to extend the mustache so that when someone walks by, they border on the whiskers.
It is sensitive enough to go easily, but not so sensitive to the cause a trigger condition whenever the wind blows or al sheet passes in front of him.

Have fun!