Originally Posted by LittleBigMan
I'm all for equalizers. I use a whistle. It's very useful to have a loud sound device (whistles are illegal, though) to grab the attention of that motorist who doesn't see you.
One drawback is that the time you use to reach for the horn might be the time you need to avoid a collision, especially if you have to remove a hand from the bars.
Since I wrote the above post around Christmas, I've rigged a 12V car horn to the homebuilt light set I put together. The horn cost about $12 and the activator button an additional $6 from a local auto parts store. It's plenty loud.
Since I already had the 12V power source, it seemed just as cheap as an air horn to add to my bike, and possibly more reliable. I've tested it in real traffic situations, and motorists pay attention to it.
I don't usually ride around pedestrians, but I will mount a small bell to alert them. I think the bell is appropriate for them, but for cars, a horn is necessary.
(I carry the whistle in my pocket as a back-up.)
Next, I'm replacing my rear LED's with a red 12V light.