This is a simple instructable that Transforms a normal fire extinguisher into an air tank for an air-horn. and Yes it is loud. you can get about 10 good blast between fill ups.
Step 1: Materials
1) Fire extinguisher with rubber hose for a nozzle
2) Air Horn
3) Air fittings that fit the air-horn and a barb fitting to fit the hose
4) screw on valve stem
5)Hose clamps to attach the horn and tank to the bike.