Pest A Cator 2000 is not an ultrasonic product. The electrical wiring inside your home already has an existing field surrounding it. When Pest A Cator is plugged in, it pulses this field. It doesn't really add to or take away from the field - just pulses it. Rodents like to live and nest inside the walls. They feel the pulse and don't like it, so it drives them out. This means that if there is an infestation of rodents, the consumer will see more during the first four weeks or so, because the Pest A Cator is helping drive them out of the walls. We recommend using traps of your choice the first few weeks to help clean up the initial problem. Additional units are recommended for larger single level areas or multiple story structures.