pair of horns

Your PM box is full. :-)

I don't know if you have looked into the airhorn thing much yet, but there are some really good kits out there that have thier own 12v compressor and all accesories needed to run them.
I can tell you from experience they are very loud.

Chk this Amazon search out.
http://www.amazon.com/s/?ie=UTF8&keywords=car+air+horn+kit&tag=googhydr-20&index=aps&hvadid=31144738370&