Your Eliminator Ultrasonic Pest Repeller works with a standard 120 Volt wall outlet. Simply plug it in and the LED Red light comes on to let you know it is working. It emits high frequency ultrasonic sound waves that help repel rodents. Varying ultrasonic sound waves prevent rodents from getting used to the pest repeller sound. Ultrasonic sound cannot penetrate walls, cabinets, or furniture; therefore, multiple units are needed for multiple rooms.