with this style pfd if it auto inflates it does not have to be worn to count as a life jacket, the ones that are pull cord only have to be worn at all times. there is 2 styles of auto pfd, 1 inflates when it gets wet (this is the cheaper one, i have heard of guys saying they have gone off in storage because of high humidity and their lockers getting wet) the 2nd one which is significantly more expensive (220-250) inflates based on atmospheric pressure is around 13lbs and every 33 feet below the water you add another 13psi... not sure how far below you have to go but i'm guessing it is only a .5 to 1.5lb pressure increase to get it to go off (this is the style i chose because I didn't want to deal with accidental inflation) i got the mustang HIT one