3 Pack, Dual-Wave Pest Repeller uses Ultrasonic wave & Elec-Magnetic wave. It is effective up to 1000 square feet. Durable, Low Energy Cost and Non-Chemical. Vibrating Magnetic Wave repel pests effectively. Pulsed Supersonic Wave is a high pitch sound that is unheard by humans but frightening to mice. Easy to operate, just plug in wall socket. Harmless to Humans, Pets, Household Electric Products and Computers Durable, Low Energy Cost and Non-Chemical.