If you plunge into the sea to ogle exotic wildlife, why not stay a while—and get an even closer view? Cave-diving engineer Bill Stone [see "Journey from the Center of the Earth," February 2007] makes that possible with the most user-friendly version yet of a rebreather, a device that recycles your exhaled air, removes carbon dioxide, and adds oxygen. (A scuba device quickly burns through tanks of fresh air.)
On a typical dive, the Poseidon Discovery lets divers stay underwater at least three times as long as scuba gear can, and since you don't exhale into the water, you don't create bubbles or noise that can scare off fish.
Military and advanced divers have used rebreathers for decades, but they're pricey rigs (about $10,000) that require extensive training on how to manually mix gases in case the gear fails. Stone's recreational model automates the safety system with built-in computers that check all components pre-dive, plus two oxygen sensors that monitor the gas mix. If the system spots an air-recycling malfunction, the mouthpiece vibrates and blinks an alert. Just flip its lever to inhale from a small fresh-air tank and return safely to the surface.