The auto feature works when the bobbin gets wet /dissolves and sets off a firing pin that punctures the air cylinder.The vest I have has been used 6-7 years and has never accidentally inflated.It has seen heavy rain several times and when it gets wet I dry it out in the truck or camp.The comment about Amazon being the place to buy rearm kits,bobbins,or cylinders is dead on.I bought 3 sets and have never had to use them. It would be hard to go back to wearing a conventional jacket but do carry them in the boat.