"And now for something completely different" Perry's are pealess, hard plastic, virtually indestructable and shrill ; qualities common with an old english girlfriend ;O) Ask the people who should know,
www.rnli.org.uk/home.asp I located a disabled canadian boater who used one. Even in high winds a whistle's note is very distinctive. Don't ask me about measured decibels. All I know is I heard the thing ( helps to actively listen too.)