I have the same reaction, even if I have to ring repeatedly. The advantage of a bell as I see it is that most people react to human speech directed at them by engaging with the speaker... without even thinking about it. So when you say, "On your left," the first reaction most people have is turn their head to the left (and often the body follows, which is the worst possible reaction). The bell is a mechanical greeting with no invitation to respond. Therefore any response is voluntary- a greeting or a thank you from the person being passed. This seems so much more civil than saying, "On your left," which is often said with a tone of voice that connotes, "GETTHEHELLOUTTAMYWAY."