Fox 40 Classic Whistle with String 9903-1308 The Fox 40 Official Classic is the world's number one professional referee whistle . It's used by 90% of referees worldwide. It's also a great tool for all coaches and is also very useful for teachers. It's perfect for referees and coaches of all levels. It's reliable in any situation where it needs to be heard above ambient noise, roaring engines, and wind. Properties: Sound pressure level: 115 dB. Two chambers facing each other. No moving parts. The string is colour-matched to the whistle. Whistle color: neon yellow. String included: Breakaway – elastic drawstring with an adjustment system and snap closure at the neck, which allows for quick release in case of emergency. The Fox 40 is the official whistle of the NBA , NHL , NBL , NCAA , FIBA , FIVB , and other federations. The Fox 40 is a ballless whistle with internal channels that produce a very loud sound. It is also used by law enforcement agencies. It is very useful for sailing, windsurfing, mountaineering, and other areas where a loud signal is needed. In the USA and Canada, people use it as a safety whistle .