For what it is worth we have started using the battery powered ultra sonic repellents and have had no problems since starting to use them. I will say that I firmly believe they will repel mice/rats but if they are already there it takes longer and trapping them to get them out. Since we finally got rid of them I haven't had a mouse/rat in the trailer once we started using the repellants. Do I believe that there aren't any at all? Nope, but they sure aren't in any of the living areas or areas I can access to check for them.