That's the Stebel Nautilus, a really common air horn upgrade for motorcycles (which is what it was actually created for). Both are very compact and would easily mount to either the actual bumper (behind the bumper cover) or to the cooler bracket which mounts the radiator and condenser. It will require a separate relay, but you can use the existing wiring to draw power.
It's a well made unit and very loud - 139db !
Hear it here:
http://www.youtube.com/watch?v=lQqxhRQ1rPE
http://www.youtube.com/watch?v=chU5LhgdEm4&NR=1
Check for it on Amazon and you may find it cheaper than Griot's (Griot wants to send his kid to Havard).
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