When a honk is not a honk
It's a given that if you get into a car or similar vehicle in this day and age, there will be a large mashable area on your steering wheel. If you should apply sufficient force, then it will create quite a racket outside your vehicle courtesy of the horn. Smack it and get a honk. Easy, right?
I think it's missing something, since it puts too many events in the same category. As far as your horn is concerned, "you're about to merge into me at 70 MPH because you didn't shoulder-check" and "the light has been green for long enough and you haven't even let off your brakes yet, wake up!" are the same thing. To me, there's something wrong about that.
Big problems should have big noises attached. That part is handled just fine right now. What I want to see is some kind of secondary noise which amounts to "oh, hey, uh, c'mon, wake up?" without causing a scene. Maybe it could be one of those silly old-time "AWOOGA" horns. The whole point is that it would be distinct from normal horns, and it would be clear that you weren't angry but rather just wanted to get their attention.
Right now, the only way to approximate that is to tap your steering wheel's horn trigger and hope you manage to hit it just enough to sound without having it last too long. You might be aiming for just a "toot" but it could totally wind up being parsed as a "HONK".
For the sake of making a simpler interface, it might be interesting if this was implemented without adding any extra buttons. Automakers could use a simple time-based detector. If it turns out that a short tap is what people are already doing to convey this message, then mapping that to "use secondary noisemaker" might just do the job. Then, if it's still down after half a second or so, go ahead and use the normal horn and make obnoxious noises.
It would be really interesting if it only made a noise for the one car you really needed to "reach", but that's just ridiculous. Having a secondary noise should be just fine.