Have you ever been underwater on a dive and had your buddy come up to you, with a wide-eyed look, spit out his/her regulator, give you a quick out of air signal, and pull your air source out of your mouth? It will only happen once because when you are grabbed, in this scenario, it feels like Andre the Giant has latched on to you and he won't let go! To prevent this scene, a diver only has a couple of options.
First, one can back off and signal for the other diver to go up to the surface. The problem with this method is two-fold though as you might have already been grabbed or it is a loved one who is on dire straights. Second, a diver could share air with the victim and return to the surface with them, however, if you only have one air source then you are putting yourself in jeopardy. Also, if it has been some time since the diver's Open Water class and without practicing this emergency endeavor, one might find the drill more difficult than remembered from class. In light of these options, an alternative air source is clearly the most logical answer for this dilemma. Concerning alternative air sources, there are many different models to choose from and the following is a brief listing of just some of the options available on the market.
The least expensive route with most alternative air sources is an extra second stage with a longer hose, preferably marked by a brightly colored hose. The alternative air source should be secured within the chest area of the diver, either on the right or left on the chest with the mouthpiece facing out in case of an emergency. Another option includes the OMEGA II by Oceanic which has a dual-facing mouthpiece so that it is never upside down. With this piece, prices vary from roughly $75 to over $100. Another option includes a regulator that fits on the low-pressure inflator. With this option, one extra hose is eliminated, but a longer primary hose might be a good accompaniment for this option. In an emergency, the buddy takes the diver's primary regulator and the diver breathes off of the alternative on the low-pressure hose.
There is also the Spare Air option which is an extra air source that the diver carries on his/her person. The Spare Air is a 30 breath regulator and tank that will have enough air for about 2.5 minutes. It works well in fresh water, but rumors of rusting in salt water are prominent. The Spare Air system retails for $195 and we have it on sale for $175.
The last option is a pony bottle with a spare regulator which provides the complete security of a full back-up system. It can attach to your tank, but does add a degree of cumbersomeness. The pony bottle is a somewhat specialized item and will work for a diver who needs more air for a deep dive. It is a small tank, however, and most shops will charge the full fill price. The price fluctuates on this item, depending on the choice of regulator, but the tank itself usually runs about $149.