Incorrect!

When should you use your vehicle's horn?

To alert others to your presence
Correct answer
To allow you right of way
To greet other road users
To signal your annoyance
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DVSA theory test explanation

You must not use your vehicle's horn between 11:30pm and 7am in a built-up area or when you're stationary, unless a moving vehicle poses a danger. Its function is to alert other road users to your presence.