Use your iPhone! Oh yeah, you're wearing a mask and are 40 meters down. iPhone barely gets bars in a tunnel. So what to do? You can use Ocean Reef's ALPHA UWCP (Under Water Cell Phone). With a 40 meter cord that attaches to a module that attaches to one of Ocean Reef's masks and the other end bobbing on a buoy on the surface. As long as your cell phone has "voice dialing", you're good to go.
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