Catwatch the only ultrasonic cat deterrent recommended by the rspb cats are usually unwelcome visitors to gardens not only do they damage young plants and scare away or kill wild birds they also leave behind unpleasant deposits british made catwatch is a humane yet very effective deterrent and the only one of its kind tested and recommended by the rspb it works by emitting bursts of ultrasound inaudible to humans whenever it detects a cats movement or body heat so cats quickly learn