On the search for a decent horn for my velo  I ran across a "loud" horn by none other than http://loudbicycle.com/    It was a kickstarter which I funded last year; it took them over a year to deliver but it arrived last week.  
 
The milan didn't come with a horn, and the mango's horn might as well be labeled "Fischer price" as it sounds like a toy car horn and is about as loud.   A lot of people have adapted airzounds with remote relays but those have been problematic    
 
For the record at point blank range to my cheap chinese sound meter the Airzound is 124db and the Loud is 122db  and the loud sounds a lot more like a car horn than a stadium blaster.  
 
Here's pics  
 
http://imgur.com/a/JhkkI
 

Cool,   I use a zound,  but annoyed at how often I have to replace it had looked for alternatives.   I hadn't found this alternative.  Looks promising though.