Kent found the one place that the horn could fit horizontally without getting in the way of folding. He says:
"I'm not using the extension yet - it just barely reaches without it, although I'm thinking of using it so I can move the trigger higher on the handle bars. It's louder than my car's horn!"
Davide Meneghetti took a different approach and mounted it to the stem. This method is less good for the water - resistance but so far it looks like it can work!
Anders from Sweden found a clever alternative solution to mounting, he said:
"I used the fastening holder from the smallest Brompton front bag modified it with a makeshift solution. The assembly is big but can be removed in an instant. I will use it in city traffic surroundings."
Set up to ride
If you choose to go with Anders solution you will need a Brompton front bag attachment and a makeshift strap. To use Davide Meneghetti's solution you only need the horn, and for Kent's top-tube mount you need a horn and but a button cable extension cable will be helpful.
You can order a Loud Bicycle horn at the Loud Bicycle Store.