What is a Horn?
The simple electrical warning device you press to alert other road users
Simplified animation — not to scale.
In plain English
The horn is an electrically-operated noise maker mounted behind the front grille or bumper of your car. It's a legal requirement in the UK — every car must have a working horn that produces a continuous, uniform sound — and it's checked as part of the MOT test. Most cars have a single horn, though some have two (a high note and a low note) to produce a richer, more attention-grabbing tone.
"Think of the horn like an old-fashioned doorbell. Press the button and a small electromagnet hammers a bell repeatedly to make a noise. The horn does exactly the same thing, just much faster and much louder — and like a doorbell, if the wiring corrodes, the button sticks or the bell itself fails, nothing happens when you push it."
How it works
When you press the horn button on the steering wheel, you complete a low-voltage circuit that activates a relay. The relay then sends full battery current to the horn itself. Inside the horn is an electromagnet that pulls a metal diaphragm rapidly back and forth — typically hundreds of times per second — and that vibration produces the sound you hear, amplified by a small trumpet or resonator. As soon as you release the button, the circuit breaks and the diaphragm stops vibrating.
Signs of trouble
- ⚠No sound at all when you press the horn button
- ⚠A weak, muffled or strangled-sounding horn
- ⚠Horn sticking on after you release the button
- ⚠Horn only working intermittently or when you press extra hard
- ⚠Failing the MOT specifically because the horn isn't loud enough or doesn't work
- ⚠A buzzing or rattling noise from the front of the car when the horn is used
£35 to £120 fitted
Always get a written quote. Prices vary by car, region, and parts brand.