Ocean Reef M101A G.divers Underwater Receiving Unit YellowThe 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 uses a 9V alkaline battery and has a low battery alarm which beeps every 30 seconds when the battery is low. Features Receive only unit operating on one channel Fits on any conventional mask strap or FFM models (mask not