Even if it's the law most states don't enforce it. California at one time required a bell and in the 30 years I rode a bike I never had one, now I'm in Indiana and the law still says a bell is required by law, but I still don't have one after being here for 13 years and I don't know of anyone who does have one, the only bells I ever see are on Electra bikes but those come with them I think.

It's easy enough to find out if a bell is required by law and being enforced...does a large percentage of cyclist have one?

I think bells are useless, first off a car will never hear it, so who is it intended to warn? Pedestrians, ok except most of them today have earplugs in so they're not going to hear it, ringing the bell takes a hand off a brake that I could be using to stop quicker with, my voice is louder than any bell. So I don't see the point. If the law wants to require a noise maker on a bicycle then it should require something that puts out at least 110db like an air horn.