This is the OTS Guardian Scuba Diving Mask & OTS-BUD-D2 Buddy Phone Communications Package Features: Nominal Range: 50 to 500 meters depending on sea conditions & noise levels. Transmission Type: Ultrasound using upper single sideband (USB) Transmit Output Power: 0.5 watts PEP Standard Frequency (PEP): Recall & tone: Freq. A (Channel 1): 32.768 kHz USB Freq. B (Channel 4): 31.250 kHz Audio Bandwidth: 300 to 3,000 Hz Automatic Gain Control: Greater than 80 dB Earphone: Ceramic Microphone: ME-16R Hot-Mic (Dynamic) or Super Mic (Standard)(Ceramic) Transducer: Ceramic cylinder Battery Type: Alkaline 9V. Batteries not included. Maximum Operating Depth: 130 feet in sea water (fsw) Weight in Air: 8.1 oz The Buddy Phone D2 is a digital, micro-miniature, ultrasonic transceiver allowing communication between two or more scuba divers or surface stations. Using Digital Signal Processing" (DSP) techniques, the Buddy Phone produces uncompromising speech clarity.The Buddy Phone D2differs from our standard Buddy Phone in that it is digitally controlled and has some fantastic new features such as: a voice menu to guide you adjust your Volume, change from Channel A to Channel B, or put the Buddy Phone in a continuous voice transmission mode. Voice Menu: When you submerge with a D2 Buddy Phone, you will hear the voice system say "Buddy Phone ON, frequency A (B), channel one (four), volume High (Medium, Low)," depending on the prior dive's settings. Changing a setting is easy and can be done while underwater. Depress the Push-to-talk switch (PTT) three times quickly and hold the third depression until you hear "main menu - volume, channel, continuous transmit." When you hear the main menu selections, simply depress the PTT to select one of the choices. The unit will make the selection and go back to the receive mode. If you don't make a selection after the menu repeats twice, the D2 Buddy Phone goes out of the main selection menu and back to the receive mode (see operators manual for a more detailed explanation - note: continuous transmit mode allows the user to talk, hands free. This was requested by many movie makers and scientists who talk on camera often). In all, this D2 Buddy Phone is State-of-the-Art and OTS technology at its best."