Clean up the home. While the device is designed to repel rats, taking basic precautions to prevent an infestation is as important as using the ultrasound device. Clean up crumbs immediately and remove trash from the home. Constant vigilance makes the home less inviting for rodents.
Check the home for rat entrances. Rat entrances include vents, ductwork, pipes and even windows and doors. Seal up any areas the rats might try entering. The problem with the ultrasound devices is that they have a limited range, meaning the rats might come into the home on a different floor than the device is located.
Plug in the ultrasound devices for rats in the house. These plug directly into wall outlets. Put at least one device per floor or put them according to square footage suggested by the device. Avoid putting the ultrasound device behind a couch, curtain or other piece of furniture because these items can disrupt the sound waves and shorten the range.