Originally Posted by
ax0n
Or you could get the marine boat compressed gas horns, if you don't mind pissing off the environmentalists by venting greenhouse gases.
AirZound makes a handheld unit that runs on compressed air.
The marine air horns don't work when it gets really cold because the gas doesn't expand enough. Not sure about how well the AirZound does.
I bought a car horn to mount on my bike years ago, but never got around to it, and probably never will since I don't think I'd have occasion to use it more than once a year or so.