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I want something that I can do at the beach without having to have my equipment.
Spare Air is still compressed air, and all of the same precautions that are learned in diving still apply. I don't see any indication of whether or not you are trained/certified on scuba.
And before you say anything about it being used in shallow water, it is possible to suffer lung expansion injury by surfacing from just 4 feet while holding a breath of compressed air.
Also, it may be uncomfortable/unwieldy to hold that cylinder in your mouth for any extended length of time.
But along the lines of diving with just a pony, Spare Air does now have a complete system that may pique your interest.
EasyDive - Dive More - Dive Faster. The ease of Snorkeling with the versatility of Diving
Probably the most unique feature is that their is one switchable mouthpiece attached to both snorkel and to regulator.
He shows 25-49 dives.Are you a certified SCUBA diver?
If not its a bad idea to breathe compressed air at depth then safely ascend without exhaling. Gooole Air Embolism for what could happen.
A Spare Air is in fact a mini-scuba system.
Contrary to what you saw on Baywatch...
If you want a beach toy, besides the one linked above several companies make affordable sNuba systems - air is fed from a compressor floating on the surface to you at depths of up to about 30? feet.
Notice that disclaimer at the bottom of the EasyDive page?
EasyDive is recommended for underwater use by certified SCUBA divers only.
I know someone who dives a 19cu ft pony in a sling while doing maintenance on his boat. In warm water in shorts. He might have a soft weight pouch clipped to it also.A pony is better. you also need a way to carry it (google "monkey diving") and probably some weights.