Usually the Dive Supervisor lets everyone know his plan before diving. It has been accepted by most commands to use the Solid Tone as a way to alert divers a voice communication is to follow or stay on the bottom until further notice. An intermittent Tone means to return to the surface. DRS-100B also allows you to record marine or made made noise, play music to all divers within range or send scientific sounds into the water. All divers within range would hear the sound.
Directors love the fact they can talk to the cameraman and all personnel in the water.