Been around for about 15 years.. I think they are still sold..

These are inflateable bags that are installed inside the boat in spare (is
there such a thing) areas, like up under the deck..

We looked at an item like that about 5 years ago at the boat show in
Chas, SC. It looked like a great idea. We saw the bags installed in the cabin
behind the settees and along side the hull on the fore peak. I believe they
were lanyard actuated. The big thing though, I heard that they were taken off
the market for a safety reason. I haven't heard about them since.

Leanne