LaMouette has developed an airbag system. A purpose designed LSA airbag systems designed to be portable from aircraft to aircraft. Key components include an auto-sense G-force and impact meter with patented cold gas inflation technology for enhanced safety. For more information see
http://lamouette.com/en/aerobag.php
It looks to be about $1500 US + VAT. Good deal, I think we should all wear one.
I wonder if it will interfere with a life vest or vice versa- maybe it could almost be a life vest when inflated ; )