The buzzer is a set of underwater and above water speakers that are controlled by the chief ref. The chief ref will sound the speakers to start the play, either at an advantage puck or at the start of point. The chief ref will also sound the speakers if a foul has been called by any of the refs, including the chief ref. This will signal to the players that the play has been stopped.
In tournaments with more than one playing area, each playing area will have a different sound produced by the speakers and players will have to be aware of which sound is being used in their playing court. If the players are unsure of what sound is being used in their playing area they may ask the chief ref for a sound check before the game.