I also have a normal bike bell that works fine on pedestrians and other cyclists. I never use an air horn on a pedestrian unless there's no other way to get them out of the way in time.
The one time I horned a pedestrian that comes to mind was like that. This guy was walking distracted and he decided to come off the sidewalk and directly into the bike lane without looking perhaps 20-30 feet in front of me. I was traveling around 15 to 20 mph. I hit the brakes hard but immediately knew I would still hit him unless he jumped out of the way. That's where the air horn came in. He jumped out of the way. No harm to him aside from perhaps some temporary tinnitus. Horn use was unavoidable in my view.
The one time I horned a pedestrian that comes to mind was like that. This guy was walking distracted and he decided to come off the sidewalk and directly into the bike lane without looking perhaps 20-30 feet in front of me. I was traveling around 15 to 20 mph. I hit the brakes hard but immediately knew I would still hit him unless he jumped out of the way. That's where the air horn came in. He jumped out of the way. No harm to him aside from perhaps some temporary tinnitus. Horn use was unavoidable in my view.