Wind Activated and easy to mount; Radiates a high-pitched sound to deter unwanted animals while driving; Will not disturb passenger or pets in vehicle. Black Deer Alert. Deer alert creates sound waves that warn animals of oncoming traffic keeping you and other passengers safe from animals darting out in front of your vehicle. This special technology radiates a high-pitched whistle which deters unwanted animals from your vehicle ensuring a safer drive. Designed specifically so only animals outside the vehicle can hear the whistle; passengers and pets inside will not be disturbed. Wind Activated and easy to mount. Help prevent injuries and costly repairs from animals with a Deer Alert by Custom Accessories. This deer alert animal warning whistle radiates sound waves that warn most types of animals of your oncoming vehicle. Passengers and pets inside your vehicle will not hear the high-frequency sound.