I have been looking, and found a copy of this Ear Cannon Air Horn (http://www.aerostich.com/ear-cannon-air-horn.html) here in Taiwan. From the website description and comments, it looks promising...
"This is a full-power railroad locomotive/ocean liner type compressed air horn squeezed into a bike-mountable package. Totally overkill, until you need to wake up some lethal driver. It’s got both the high and low ear-splitting tones of the individually sold Fiamm Freeway Blaster Horns, plus a little more oomph. The 139dB high and low tone blasters combine via air induction to cut through the din and make the most distracted of drivers drop their cell phones and pay attention. Installs easily on all bikes with a 4.5"×3"×4.5" space for mounting. The loudest motorcycle horn available. If Ethel Merman, Sam Kinison and John Philip Sousa ever had a band, and played through a wall-of-sound amp rack, it would sound like this. 12V. 1 lb 4 oz."
And this one:
"It makes small children cry (or make that trucker-honk-your-horn gesture), bad drivers soil themselves, and that teenage girl with the gigantic sunglasses who pretends no one else exists dump her double latte right down the front of her pretty little blouse and all over the seats of Daddy's SUV."
Can't wait to try it! But will have to learn about relays in the mean time...
