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. Flawless, consistent and penetrating sound keeps the referee in control of the game. Be heard above ambient noise, the roar of engines, breaking waves and gale-force winds. The chambers are designed to self-clear when submerged in water. No moving parts to freeze, jam or deteriorate.