The whistle is the referee’s tool that determines how well they are heard by players, coaches, and spectators. Choosing a good whistle is important for the referee, and it is fairly simple. When I work matches, I use a simple Fox 40 whistle, and it has a good sharp sound that is sure to grab the attention of anyone in the ZIP code.
Some other types of whistles are whistles with the “pea” inside them. They do not produce as sharp a sound and I don’t recommend using them in matches.
Overall, I would say that if you choose a whistle from a popular brand (Fox 40 or Acme) and the whistle DOES NOT have a pea in it, you should be good to go and everyone watching the match or participating in it will be sure to hear you.