Ocean Reef GSM Mercury Dual Power Wireless Underwater CommunicationThe GSM Mercury Dual Power is just like the GSM Mercury, the best underwater wireless communication device by OCEAN REEF, but this time instead of having 2 channels it has the option of having channel 1 at normal power and reduced power to ensure clearness of sound also in confined waters like pools or tanks. The unit is easily recognized thanks to a yellow sticker that reads Dual Power. This unit is made to fit only on our EXTENDER FRAME. Key