Have you noticed that in US cities, when you are at a stop light and the color changes to green, sometimes the person behind will honk angrily if you do not immediately take off like a jack rabbit? That annoys the hell out of me and is one reason why I almost never use the horn even when it is the person in front of me at a stop light who has not immediately noticed that the light has turned to green. In such cases, it is often the driver behind me who horns.
With the standard car horn one has just two options: a long blast that sounds angry or a quick tap. But even the latter tends to sound too peremptory for me. Mark Rober, an engineer, does what engineers do and that is find solutions to practical everyday needs. In this clip that I found via Rusty Blazenhoff, Rober describes how he added a variety of car horns to meet specific driving needs, such as gently alerting people.
I hope car manufacturers take note and make the courtesy horn a standard feature so that we do not all have to become do-it-yourself experts. I really, really want a car horn like this.