Meet the Sound Grenade: a tiny device with a 120-decibel alarm to get you out of trouble. It weighs less than 1oz, so you can carry it around conveniently. At the same time, it has a loud siren to get you out of trouble. The siren sounds continuously for 30 minutes once you remove the pin.
The Sound Grenade works under water and in 14F to 104F temperature range. Like what you see? You can get yours for under $20.