Reduce your chances of deadly or expensive vehicular accidents with the Deer Warning Whistle. This air-activated whistle alert animals in the area that you are driving so they do not make any sudden movements, keeping your family and you safe to continue travel.The whistle to alert deer fits all trucks, motorcycles, cars and vans. Air is forced through the two whistles, creating two unique sounds. Vehicle must be moving faster than 30 mph to operate. The dual sounds set this deer warning system above the rest in regard to performance. The whistles can be easily removed for cleaning. Whistlers measure 2 inches long x 1.5 inches high.