Cars and horns, they go together hand and hand. And, as you may already know, the relationship goes back to the beginning of the breed. 

Car signalling devices go back to the mid-1800s in Britain where steam carriages were just beginning to appear. Back then, a law passed that said "…self-propelled vehicles on public roads must be preceded by a man on foot waving a red flag and blowing a horn." Of course, it didn't take much time to realize that a horn mounted on the vehicle made a little more sense.

In the early 1900s, the car-mounted horn became the attention-getting device used. A squeeze on the bulb and everybody around knew you and your car were around. 

Soon however, some people were demanding for a more powerful warning device, one that they could hear 100s of feet ahead. This lead to the development of the Klaxon horn. With its name taken from from the Greek word klaxo, meaning "to shriek," the klaxon produced its sound through an electrically-powered vibrating diaphragm. Arguably the most memorable Klaxon horn is the "Aoogha" horns on the late Model T and Model A Fords.  

Since the 1930s, manufacturers have experimented with the sound chamber and basic Klaxon-type diaphragm to make many sounds. The goal generally is to produce horns that are kind to the ear but still able to be heard over traffic's noise.  

Today, due to cars' better soundproofing, they are more frequently tuned to notes F-sharp and A-sharp that are a bit more penetrating. The design of car horns has also entered the digital era with a few car horns being really just powerful speakers driven by electronic circuitry.  But, along with such high-tech designs, the old fashioned vibrating diaphragm horn still thrives, as it simply works well and is a good example of staying with a technology that simply performs the job and does it well.