CatScram makes couter tops, plants, furniture, balconies and entire rooms off-limits to cats - even when no one is home or you are sound asleep. It utilizes a passive infared motion detector to sense when a cat nears a protected area. The unit then emits a series of strong pulsating ultrasonic waves for 4 seconds to repel the cat, training it to stay away. The ultrasonic waves are designed in the range that is heard by cats but is inaudible to humans. Cats find the sound so uncomfortable that areas guarded by CatScram are soon avoided altogether. Because cats have a mind of their own, there's CatScram!