Ok. Ok. We all know what a horn is. It’s the thing in a vehicle that typically goes “honk”. However, do we all know how a horn works? Do we all know fun facts about horns? Do we know the hilarious things that my brain will come up with that a horn is not? Stay tuned to learn!

(By the way, I’m sorry this post is so late. It’s been a busy couple of weeks here at CMAC!)


To know what the heck a horn IS as it pertains to an automobile, we must first explore what the heck a horn IS NOT. A horn is not:

  1. A vegetable that grows on stalks and is often guarded by a scarecrow
  2. The past participle of “hear”
  3. An instrument that produces a pleasant, calming sound that would put a baby to sleep
  4. Another word for elbow

So…what the heck is it then?

A horn is a sound-making device in a vehicle used to warn others of the vehicle’s approach or presence, or to call attention to some hazard. For years, they have been electromagnetically or pneumatically activated, but nowadays, they can also be digitally activated. This post will focus on the electromagnetically activated horn.

An automobile horn doesn’t typically look like the ones featured in my doodle above, unless it was on an old-old vehicle—like a Model T or something. I was just going for an identifiable image in the doodle. They look something like this:

How Does It Honk?

Electromagnetic horns work by using the scientific law of elasticity—the strain of an elastic object is directly proportional to the stress applied to it.

The horn is made up of a flexible metal diaphragm, a coil of wire connected to a contact, a switch, and housing that is typically plastic.

Horns are usually attached to the frame at the front of the vehicle under the hood. This provides an electrical ground for them. They are connected to the battery, but the electrical circuit is incomplete until the switch is activated.

  • When you press the horn-symbolled button on the steering wheel, it activates the switch inside the horn.
  • That switch completes the circuit, allowing electricity from the battery to flow through the coil, causing electromagnetic attraction.
  • That attraction pulls the diaphragm inward until the contact is opened.
  • When the contact opens, the circuit is broken, so the electromagnetic attraction stops, and the diaphragm returns to its original position.
  • Once the diaphragm is back in its original position, the contact closes, and the circuit is complete again.
  • This process happens over and over very quickly until you stop pressing the horn-symbolled button, which breaks the circuit by deactivating the switch.

The sound comes from the fast vibration of the diaphragm, and is amplified by the shape of the housing.

I know some people learn better by watching a video. Here’s a little click bait for you:

Click on this link to a video on YouTube. You won’t BELIEVE what happens next!

Fun Facts

  • In the early 1800s, steam carriages were becoming popular in Britain. For the safety of pedestrians and animals, a law was passed stating that “…self-propelled vehicles on public roads must be preceded by a man on foot waving a red flag and blowing a horn.”
  • Many states have mandates for auto manufacturers that require large trucks to have horns that are loud and low, to allow other vehicles to know that a large vehicle is approaching just by the sound of the horn.
  • A good number of collector vehicles made prior to the 1970s use two horns—one with a low note and the other a high note—creating a distinctive sound for each vehicle.
  • Up until the mid-1960s, most American car horns were tuned to the musical notes of E flat or C. Since then, many manufacturers have moved up on the scale to notes F sharp and A sharp.

I would totally have these guys be my pedestrian-powered signalers if I lived in Britain in the 1800s.


So, there you have it. Now you know what the heck a horn is NOT, what it IS, and perhaps found a new appreciation for mariachi bands.



Tell me what other automotive parts baffle you. I’ll tell you what the heck they are!

Written by Ben Scharff

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