A few weeks ago I installed a Stebel air horn on my 650. This morning on the way to work I had a pickup pull out from a side street on my left and pull into my lane heading the same direction I was. I saw him make the move to pull out in time for me to swing over into the bicycle lane and go past him but I gave him a pretty good blast of the airhorn as I passed. I could see it rattled the driver with him looking to see where the horn was coming from. After passing I got to thinking, maybe blasting the horn wasn't the smartest thing. Being it startled the driver, he could have gone for the shoulder of the road and took me out or made some other drastic move. As it was, I blew the horn as more of an automatic reflex.