Automatic PFDs - Just Add Water ?
 

How much of a soaking before it fires off? Can you be out in the surf, get wet by a wave and have them go off or do you have to be swimming for a bit? If they go off in the waves then I'm probably better off with just the manual pull type.

PFD's, the Sospenders brand can be used both manually and on automatic. When you insert the CO2 cartridge just don't add the lifesaver candy size O ring where it is placed. Then you just rely on the pull cord. One thing about the automatic function..........if you get conked on the head and become unconcious or semi-concious you will rise to the surface. I think the time frame is only a few seconds. An email to the company will settle any question time wise.

I set mine to manual but there are inflatable pfd's with automatic hydrostatic release instead of the disolving pill.

to answer your question, you can put a hose it and it wont go off, it needs to be completely submerged to go off.

Mustang...
 

... makes vests that respond to water pressure (hydrostatic pressure) to trigger them. As far as I know these are the state of the art, and you pay accordingly. Big bucks. I picked up a manual/automatic for a really good price at West Marine that I use when it's scary.

This feattue is an important one. Everyone I've spoke to that has fallen over has hit their head one way or the other.