I'd always forget to un teather and have it go off all the time. It would have to be over your life jacket, if it was under anything, just like the SOSpenders , when it blows up it would stop your lungs from expanding.
That illustration looks like it would work real well if you were going real fast in reverse on your motorcycle and hit something. In the real world and in most cases ,I'm guessing you would likely be eating some handlebars before it went off.