Getting people's attention while riding a bike is a tricky situation. I use a bell for alerting pedestrians and I always seem to be in a no win situation. When I ring my bell to alert pedestrians when I am approaching from behind I will often get dirty looks in return. And when I don't use my bell people will often give me dirty looks for not alerting them.
Riding on a mixed use path much of the time is also a challenge because many joggers will have ear buds stuffed in both ears and they are oblivous to anything around them. It would take a lot to get their attention and reader Harold from The Big Easy has one idea that would surely solve the problem of people not hearing you, but might give pedestrians a heart attack. Harold's idea might be best for heavy riding on streets with vehicles. Here is Harold's idea . . .
You can buy a small marine air horn at any good boat/fishing store. Academy Sports, BassPro, Cabela's etc. The whole deal is about four inches long with replaceable screw on cartridges that are about an inch in diameter. I guerilla taped one to my handlebars withing thumb reach. (you can buy electrical tape in coordinated colors if you like something pretty).
OK, at this point I've got to state that I'm not sure if air horns of any kind, are legal here in New Orleans, but this little unit can sure stop a speeding beer truck before it crosses into the intersection on you.
Harold's idea reminded me of a horn called the Airzound. It is a canister that will fit into a water bottle cage and is meant to let out some serious sound.
Here is a very good review of the Airzound that I found on YouTube.
And here is a set up that will likely alert people in the next zip code that you are coming.
Have you discovered an effective and/or creative way to alert those of your presence on the roads/paths? Feel free to let us know.