The one I built from a Mainstays light kit sensor and a Canon Owl PF Date. Using the power output wires without a latch causes the circuit to be made and broken whenever movement occurs. Sometimes it's so quick that if movement is too quick and short, the camera won't go off at all.

I got the plans from Jesse's Hunting Pages, if you want to build one. It's not really cost effective anymore as you can get similar quality 35mm cameras like the MC2g for less than 60 bucks. But if you're looking for a project and have a bit of electronic savvy it can be fun.