FOX 40 CMG Official Classic whistle + string 9601-0008 The FOX 40 CMG Official Classic is the world's best 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 . The FOX 40 CMG Official Classic has a unique sound because it is a ball-less whistle. It is constructed of plastic. It has a rubber mouthpiece and a string for hanging around the neck. Loudness : 115 db The FOX40 is the official whistle of the NBA , NHL , NBL , NCAA , FIBA , FIVB , and other federations. The FOX40 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 US and Canada, people use it as a safety whistle .