[pearlthehedgie]

I've wondered the same thing. We used to use something similar and I unplugged them all. I have seen though that the ones that emit the sound cannot go around obstacles, through walls, etc.---don't know if it's true or not so we unplugged just to be safe. Hope you get a better answer. There is also something that plugs into an outlet and uses the wiring in your house to make an electromagnetic pulse to repel mice....we definitely unplugged that because it seemed to affect everywhere from what I read. Sorry not very helpful.