I used them for bear hunting. Really no way to really tell if they work or not over bait.
When I first got mine. I put it in the corner in the house and to test it I turned it on, then put a hotdog behind it to see how my basset hounds reacted. If you know bassets you know they can smell hotdogs miles away.
They paid no attention, like it wasnt there. I turned it off, and bam, they had the hotdog gone in a pair of seconds.
I have to say I believe they work.