Black Decker EP1100A Ultrasonic Pest Repeller, Black Evict rats.mice.cockroaches.spiders.scorpions and other pests from rooms large and small within two weeks with this easy to use ultrasonic pest repeller from Black and Decker.The unit emits ultrasonic sounds pests can not stand.A 100 percent Duty Cycle means constant sound so.once they are gone.critters get no chance to come back.The unit works by disrupting pests nervous systems.affecting both feeding and communication.