As used by Hove Surf Lifesaving Club :)

Loud, totally waterproof, and can be heard underwater! Great for scuba divers, snorkellers and swimmers for when being heard is a matter of life and death. 

Exceeds Coast Guard & SOLAS requirements.

Colour: Orange

"World's Loudest Whistle' apparently! Do not blow near to anyone's ear or you will damage their eadrum.