Halcyon's design of the RB80 rebreather surpasses all previous standards for safety, gas efficiency, and ease of operation in self contained, mixed gas recirculating systems. Not only does the Halcyon RB80 reduce the likelihood of the most common hazards associated with existing rebreather systems, but it also integrates well with open circuit diving skills while increasing gas efficiency by approximately eight times the gas carried. An 80ft3 bottle would, on average, provide the equivalent of a 640ft3 useable breathing supply with the RB80. Halcyon's operating system is free of single point addition failures. Potential breathing supply failures are signaled by intuitive alarms which use physical indicators to make it immediately apparent if a diver forgets to turn on his supply bottle or runs out of breathing gas. These alarms can only be used with Passive Addition systems, like the Halcyon, that force a diver to breathe off the bottom of the counterlung because part of his previous exhalation has been dumped overboard. If the actual addition mechanism fails, each successive inhalation is shorter which gives the diver a less abrupt version of the kind of warning afforded by open circuit SCUBA. Intuitive alarms make the Halcyon safer than Active Addition (i.e. Constant Flow) units such as the Atlantis, which would continue to recirculate the same breath while the FO2 continues to drop into a potentially dangerous zone.