My dad has one of these on his bike. After my last trip to the mountains, I think I'm going to try to fit one on the XX. When someone tries to come into my lane, the stock wimpy horn doesn't get my point across well enough.
http://www.twistedthrottle.com/trade/productview/2137/93/
http://www.twistedthrottle.com/trade/productview/2137/93/