Sorry for the delay in answering, I was out riding all day yesterday!

The airhorn works wonders, and even yesterday while I was riding with a buddy, it helped out numerous times, especially when careless drivers would try to back out of a parking, or once when a driver tried to overtake and turn. Also scared the living daylights of another driver who was stopped on the side of the road with engine on, wheels turned to traffic and was fiddling with his cellphone... these drivers usually just lurch out slowly into traffic.

I've mounted/placed my airhorn in the water bottle cage located on the bottom frame, although I've seen people mount them BELOW that location, on the handlebar stem (if tall enough), even wedged under the seat. The good thing about them is that lack of weight, and the ability to fabricate or order a longer tube.

Here's a quick googled pic with the airhorn below the downtube...