Sonic PestChaser repellents emit high frequency sound waves to create an acoustically hostile environment that effectively repels rodents from protected areas. Sound is inaudible to people and nonrodent pets. Covers up to 400 sq. ft. For use in average-sized rooms, kitchens, garages, and basements. Ultrasonic sound cannot penetrate furniture, cabinets, or walls. Multiple units required for multiple rooms. Provides years of useful operation. Ideal for environments where the use of poisons is inadvisable or prohibited. Perfect for homes, offices, summer homes, boats, restaurants, hospitals, farm buildings, kennels, stables, etc. Uses less than $.01 worth of electricity per day. Plugs directly into an outlet. Does not interfere with the radio, television, or other electronic equipment. 4 pack.