When divers think of a bail-out bottle, chances are it's the Spare Air 300 that comes to mind. After all, Spare Air has been a trusted back-up air supply for three decades. Just 13 inches tall and two inches in diameter, the Spare Air 300 uses a balanced, single-stage regulator that screws directly onto the bottle. It stows in a custom holster that mounts to a BC, and can easily be deployed one-handed. The Spare Air 300 is always on, so in a pinch you just put it in your mouth and start breathing.
Fill the 300 straight from your primary cylinder in seconds via a yoke adapter. You can also fill directly from a fill station or compressor with a special fitting. A built-in pressure indicator nub protrudes when the bottle is full, or you can get an optional dial pressure gauge. If you want to be even more compact, opt for the Spare Air 170, which is the same as the Model 300, but smaller.
The bottom line: Easy to fill, stow and use, the Spare Air 300 is the perfect miniature redundant air supply system. There's even a N2 version for nitrox divers.