We have lifejackets that are supposed to inflate automatically when they get wet. They're very unobtrusive and comfortable, and we wear them pretty conscientiously (remembering the advice that lifejackets are useless unless worn!). We also have them professionally serviced every two or three years. This winter wasn't in the sequence for professional servicing, and so this week we inspected them, with the intention of blowing them up manually to make sure they were airtight.
It was a horrible experience to discover, as I unwrapped mine, that the gas cylinder had come unscrewed (despite having quite a long thread) and was loose in the lifejacket, so that, had I gone in to the water, the jacket wouldn't have inflated at all. We'd heard of this happening, but hadn't really taken the possibility seriously. It was very easy to check, and I strongly recommend doing it!
Gilliane
Miss Fidget, Super Seal 26, no. 69
Delphine, Parker 275, no. 41