A electronic rodent repeller uses high frequencies.

The electronic rodent repeller works two different ways. One type works by plugging straight into a 120 volt wall outlet and emits an ultrasonic frequency somewhere between 30 kHz and 55 kHz. These types of high frequency sound waves are too high to be heard by humans and also family pets like dogs and cats. However they are able to be heard by rodents. These sound waves create an unpleasant environment for the rodents and then forces them out. It alters the sound waves and does not repeat the same frequency so the rodent is unable to adjust to it.