I installed a compact air horn after a big rig almost ran me off the road several years ago. It's a tight fit if you have a center radiator, but still very doable. The company horn still packs a significant punch, the one I used looks similar to this:
https://www.amazon.com/Stebel-11690019-Nautilus-Compact-Black/dp/B00CMX20H4
I spliced into the wiring for the existing horns, and ran a ground to the front trunk and power directly to the battery with an inline fuse via the rubber firewall grommets. If I recall correctly the horn is 12V, but needed to be connected directly to the battery. Super simple, quick install once you have the front bumper off. I recommend leaving the original horns installed. Since the air horn takes a fraction of a second to charge, the original horns activate first which allows you to have a quieter horn for a friendly "beep beep."
