http://www.bikesonline.com/sram-bicy...bell-black.htm

SRAM makes a headset bell to go with your Force or Red

I use bells on all my bikes. Comes in handy...wifey and I ride a 10 mile trail loop that we do laps on, and although a bike trail theres still lots of pedestrians. on trails i think bells are mandatory since flying by on some pedestrian's left is a recipe for disaster. people can be clueless sometimes and step out in front of you, and its my experience people can hear a bell way farther away than a voice hollering "on your left" (unless you have an abnormally loud voice and dont mind a hoarse voice after the ride)....i try to give a ring far away, then another ring or two approaching closer, then another ring when im close to passing.

im kind of fredly with bells on all bikes but meh id rather be safe than sorry