Fox 40® Classic® 43-045 Whistle Yellow is the standard choice referees and coaches at all levels, rescue professionals and general safety worldwide. No moving parts to freeze, jam or deteriorate. Flawless, consistent and reliable. The harder you blow, the louder the sound. Easy to blow and cannot be overblown and will be heard above ambient noise, loud crowds, the roar of engines, breaking waves and thundering gale-force winds.