Car horns honk in a certain key?

The vast majority of American cars honk in the key of F.

Photo from here.

Isn't that random? I wonder if people sit there and think "Humm.. I wonder how the car horn should sound?... Maybe a E? No, that's too low.. How about an F?" Seems rather strange to me! Haha. I'm sure it must be something to do with what note sounds harshest on your ears, because they want you to react to it and not just sit there and ignore it. It's just like a fire alarm in that sense, they are really load and penetrating so that there is no way you couldn't hear it! (Well, that's the case for all the fire alarms I've heard anyway!)
And it does make sense for car horns to be in the same key, cause otherwise it would be hard to tell if it was a car horn or something else.. The brain probably associates F as a warning in America if you've heard lots of car horns.. It's weird to think about, but also pretty darn cool ;)

Sorry I've been honking on a bit, I'll leave you in peace. ;)