Fox 40's first pealess whistle. The harder you blow, the louder the sound! Reliable, flawless consistent and penetrating sound. Used by referees and coaches at all levels who need every call to be heard and depend on its reliability. Be heard above the crowds and players. Flawless, consistent and penetrating sound keeps the referee in control of the game. Ensure every call will be heard! Standard choice for personal safety and rescue professionals wordwide! It will be heard above ambient noise, the roar of engines, breaking waves and thundering gale-force winds. The chambers are designed to self-clear when submerged in water. There are no moving parts to freeze, jam or deteriorate.