The OTS DRS-100B Diver Recall Hydrophone System is U.S. Navy approved and used by Special Warfare units around the world. The DRS-100B is a dive supervisor's best friend, allowing him to recall free-swimming divers. It will alert all divers within in range with either voice, solid or intermittent tones. The DRS-100B Diver Recall Hydrophone System also offers a listening mode which is great to hear marine biological and/or man-made noise. This OTS System comes complete with a high-quality hand-held microphone, transducer with a 25 feet of cable, rechargeable batteries, battery charger and main electronic unit. The DRS-100B is a must for all diving operations! All you have to do is lower the transducer cable into the water and all divers within range and same frequency will be able to communicate.