A Diver Recall System is primarily designed to alert, recall or send voice communications the diver/s.  Some of the better units incorporate a listen mode designed to listen to marine or man made noises in the sea.  A basic system consists of an electronic package, power source, transducer and some sort of microphone.  The set up is basically simple.  The user would set the electronic module in a convenient and safe place, lower the transducer in the water and power the unit up.  It would depend on the system to what choices he has to choose from.  All Divers within range would hear the communications via their naked ear.  No listening device is required.  That is the main difference between a Hard-Wire or through-water system where the divers is required to have some sort of receiver to listen.

To further present how a system works, we will use a DRS-100B Diver Recall/Hydrophone system as a model.  The DRS-100B is designed to allow a user to talk with voice communications to all divers within range.  It does not matter how many divers as long as they are in voice range which is about 100 yards.  The user simply sets up as described above and uses a hand-held push-to-talk microphone to project his voice into the water.  The divers hear the voice similar to hearing a page in a supermarket.   The user also has the choice of using Tones rather then voice. Tones will travel farther in the water then voice.  The DRS-100 has an Intermittent or Solid Tone.   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.  The user also has the option to listen to all noises being made within range of the speaker (i.e. Whales, Dolphins, made made, etc.).

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.  The DRS-100 is popular with Military commands around the world for diver safety and has been used on many Movies! Directors love the fact they can talk to the cameraman and all personnel in the water.