Cats Can Be A Real Nuisance In The Garden & Although Nothing Is Cat Proof, The Ultrasonic Cat Scarer Is A Great Way To Repel & Discourage Them. the Ultrasonic Cat Scarer Features A Pir Motion Sensor That Works Day & Night To Detect Movement Up To A Distance Of 40ft Before Emitting A Powerful Ultrasonic Whistle That Is Inaudible To Humans, Other Animals & Pets But Is Unbearable For Cats. Battery Operated (2 X 9v Not Included), Simply Locate The Ultrasonic Cat Scarer So That It Faces Towards The Garden & Pre-set A Frequency.ultrasonic Cat Scarer Measures 20cm X 13cm X 13cm Hbattery Operated (2 X 9v Not Included)