This new Heron Deterrent from Velda has a motion sensor which will detect movement at an angle of 180º & a radius of up to 25m. When the sensor detects movement it makes a loud piercing noise (which sounds like a bird of prey) & the light flashes on & off. The combination of the loud noise & the flashing light startles the heron & scares it away. The deterrent will also scare away other pests such as cats.