Bicycle Bell?

If you're on a shared path, dinging the bell 5 or so seconds before you pass a pedestrian/rollerblade/jogger is the considerate thing to do. People seem to associate the "ding ding" with a bike, so they don't get startled when you pass them.

For everything else your voice is probably better.

oh okay thanks!

a "ding-ding" followed by "on your left (or right)" can keep it a good day both ways.

I think it's only polite to "ding ding" when approaching a pedestrian from behind. For everything else, the ungodly squeal in my front brakes is warning enough!

If forced to pass a pedestrian I like to go up a couple of gears the get out of the saddle and accelerate rapidly, this way by the time the ped's brain has had a chance to panic and make them jump the wrong way you will hopefully be ten yards or so past them. Be wary of anyone with a compass on a cord around their neck or hiking with ski poles (what the fah is that all about), these people tend to be militant bike haters. If possible pass these types where there is water/feces on the trail and kick out your rear wheel a couple of inches in their direction.

It's best to roll your eyes and ding the bell incessantly when the only parking meter you have to lock up to is at a handicapped spot.....