This isn't home-brew. It's the new mini airhorn with stock horn/highbeam controller from Screaming Banshee. I have the old setup, and this is just the compact version.
They're great. Scared an idiot back into his own lane just yesterday. Excellent tool.
Young enough to know I can. Old enough to know I shouldn't. Stupid enough to do it anyway
'13 Duc Multi GT, '10 Vstrom 1k, '07 GSA, '10 KLR, '02 Yam TW200