This article lacks explained warning against wireless communication. This due to deflecion and reflection of sound through water levels with alternating density due to changes in pressure, salinity and tenperature. Also obsticals and topography may cause disruption or «shadows» that cut the connection between micropones on the diver and on the surface. Dangerous to the diver and also to the work. Wireless comms may work well between divers being close and at the same deaph or level with equal density and acoustic properties. The physical law of reflexion through matters, Snell’s law, explains how this may be different and dangerous when the microphones are apart. Wireless comms is preferred in stead of safe cable comms to avoid physical connection to surface - life line. A diver in trouble, such as with gas cut, should both be heard by collegues topside and be pulled to safety. If stuck, at work, rescued by the stand by diver.