Bests & Worsts Reviews from Amazon

This repellent has 3 levels of sound. It is placed inside my house close to the back door. I turn it up to level 3 at night and even I cannot tolerate the sound it emits. Once morning early, while it was still a little dark outside, I opened the back door to let the dog out but did not change the sound level to level 1 as I usually do in the mornings. As I stood at the door waiting for the dog, I heard a crying sound like a squeak coming from the AC condenser. Th sound kept getting louder, stronger like a wailing. Finally a rat shot across the yard from behind the AC condenser into my neighbor's yard. It moved so fast, split seconds. My guess is that it heard the sound coming from the repellent and could not take it. While this repellent does not stop the rats from coming into my yard (since it is placed inside my house) it will definitely stop them from coming into my house. If by some miracle they make their way in, they will leave. I wish the manufacturers would make one that I can place outside in a covered outlet.