I think every new car should come with a two horn option. One horn would be the standard blaring one that all cars are equipped with currently. You know the one that scares the crap out of you when you are stopped at a light and don't notice the change? That would be the one used to alert a driver to a real danger.
The second one would be a sweeter , gentler, softer sound that would casually alert the driver that perhaps their attention is needed. This would save a lot of lives as well because it would keep you from having a sudden heart when you are lost in thought and the danger horn is sounded from behind you.
I am just saying as a middle aged woman with a lot on my mind a gentle reminder to come back to reality would be appreciated.