Whistles are for emergencies, bells to get someones attention. Can you imagine if there were whistles at the service counter instead of a bell? Yikes!
I just put a bell on my bike and noticed even the squirrels get out of the way faster than if I yell.
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FB4K - Every October we wrench on donated bikes. Every December, a few thousand kids get bikes for Christmas. For many, it is their first bike, ever. Every bike, new and used, was donated, built, cleaned and repaired. Check us out on FaceBook: FB4K.
Disclaimer: 99% of what I know about cycling I learned on BF. That would make, ummm, 1% experience. And a lot of posts.