Reduce your chances of deadly or expensive accidents. Deer Warning Whistles alert animals in the area you are driving. Provides safety for you and your passengers. Fits all trucks, motorcycles, cars and vans. Vehicle must be moving faster than 30 mph to operate. Air is forced through the two whistles, creating two unique sounds. 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.