Bicycle bells are mostly for warning pedestrians when approaching from behind and passing on shared-use trails. I ride on shared infrastructure and cannot afford to build new infrastructure when my town will not. Not warning a pedestrian when approaching from behind introduces the possibility of collision if the pedestrian makes a sudden change in his walking course. I typically use this etiquette:
Passing a single pedestrian or runner on a quiet day: no bell, coasting for a short bit with a loud free hub (the rotating ratchet element on the rear wheel) alerts the pedestrian to my presence.
Passing a runner: normal ring from a distance so they have knowledge that the bicycle is passing
Passing a cyclist: one loud ring from a distance
Passing a pedestrian walking a dog: two loud rings, one far, one close, so that the pedestrian is aware of the approaching bicycle and he can prevent his dog from running at me/colliding. Many dogs do seem to enjoy a bicycle chase.
Antisocial pedestrians (i.e., walking side-by-side such as to be blocking the path in both directions, preventing the bicyclist from passing): several loud rings of the bell until the antisocial activity has abated. Announcements in my local tongue (not English) that they impede the flow of traffic.
Passing a single pedestrian or runner on a quiet day: no bell, coasting for a short bit with a loud free hub (the rotating ratchet element on the rear wheel) alerts the pedestrian to my presence.
Passing a runner: normal ring from a distance so they have knowledge that the bicycle is passing
Passing a cyclist: one loud ring from a distance
Passing a pedestrian walking a dog: two loud rings, one far, one close, so that the pedestrian is aware of the approaching bicycle and he can prevent his dog from running at me/colliding. Many dogs do seem to enjoy a bicycle chase.
Antisocial pedestrians (i.e., walking side-by-side such as to be blocking the path in both directions, preventing the bicyclist from passing): several loud rings of the bell until the antisocial activity has abated. Announcements in my local tongue (not English) that they impede the flow of traffic.