The M101A G.divers is a receive-only unit operating on one channel. The M101A fits on any conventional mask strap or full face mask models. It might be held and shared by more divers thanks to the high quality speaker. The M101A's reception is so strong that, in fact, it is not always necessary to attach it to the mask strap. A diver may hold the unit or attach it to a BC, allowing other divers to listen to the transmission (dependent upon environmental conditions and distance). The unit automatically activates upon contact with the water. The M101A uses a 9V alkaline battery and has a low battery alarm which beeps every 30 seconds when the battery is low. The M101A unit's total battery life is approximately 30 hours and is depth rated for 120' (40 meters) with a operational range of 600' (200 meters).