I have twin air horns and remote compressor on both my bikes and also the car , only about £12 from e bay
The horns fit nicely behind the front fairing panels ,with the compressor, cable tied to the top hose, almost out of sight.
They need a relay and have blown a 15 amp fuse so I use a 20 amp blade fuse.
Great feel good factor when someone is reluctant to move over after an ovetake, never failed yet!