Originally Posted by
Jim from Boston
Thanks for your reply. I have not tried using an airhorn because I wonder if in a tight situation, where I would have to do a quick evasive maneuver, if I could further react to blast the horn. IMO, more likely it would be a post-event reaction. 
As far as the air horn goes, placement is key. My lever is at the end of my grip, in front of my brake lever. I can rest my thumb on it comfortably while riding in situations where I anticipate the need (like Costco's parking lot, when I shop on my bike, to alert drivers backing up). It actually saved me once at Costco; a guy in an SUV backed up with his music blaring and windows closed and he did not see me, but a long blast and he stopped on a dime!!! I didn't have anywhere to go with cars on the other side so it saved me getting squished. I use the air horn as an alert to drivers in situations where I'm not sure they see me, it's not so much an emergency thing as a way to prevent that emergency. Drivers do not hear bells and a quick horn tap gets a head turn so I know they see me. Just my experience...