Last week, Karl Shreeves and I were on Grand Cayman, taking part in Inner Space, a week of diving with and talking about rebreathers. It was a good place to see the spectrum of units available in action. Some were standard production machines, some had been heavily modified by the users. Although CCRs take considerably more time to initially set up, and more care on the part of the diver to use, they do come into their own with extended deep diving, effectively giving optimal mixes regardless of depth. Quite a few dives were routinely made down to the 100 metre level that week, a depth that was fairly extreme not long ago. Some interesting developments were discussed during the evening presentations; it was especially significant was that a working CO2 detector was undergoing final tests on one unit there. Such devices will significantly increase CCR safety if they are practical and reliable.