Protect your home or business from mice and rats without using poisons or traps. Once plugged in to an ordinary electric socket, the Repeller produces over 100 decibels of ultrasound that, although inaudible to humans, dogs or cats, will send mice, rats and other rodents racing for the door. As ultrasound cannot pass through solid doors and walls, each unit is effective only in the room in which it is plugged in.