A new twist on pony bottles, and spare air is the H2O Odyssey Extra Air System.

Pressure Gauge for use with bottle.

The heart of the system is a unique regulator, that is threaded to screw directly into any standard thread scuba tank... from a little 6 ft pony - up to a full 80 or higher. For years people have wanted to have a system where they could have emergency backup air - but for some, the hassle of buying a pony bottle, plus valves, a first stage, second stage, hoses, etc.. Made the whole thing too complex and cumbersome. And some, while liking the Spare Air worried that a 3 cubic foot bottle was not enough air depending on depth and the need for safety stops.

This Extra Air comes equipped with a Balanced Piston 1st stage - with threads to fit any standard bottle. It has 2 low pressure ports and 3 high pressure ports. You can buy the first stage by itself, get any pony bottle, and hook up an octo and have an instant pony system. Or get it with the integrated swivel 2nd stage which has dual silicone exhaust valves which directs bubbles away from mask and has a high grade silicone mouthpiece.