Beep

google

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1920s: imitative.

wiktionary

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Onomatopoeic. (This  etymology is missing or incomplete. Please add to it, or discuss it at the  Etymology scriptorium. Particularly: “how old is this word?”)

etymonline

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beep (interj.)

1927, imitative of automobile horns (originally of the sound of a certain type of automobile horn, one among several in the years after the klaxon horn first was brought into use c. 1910). Used as a noun and verb by 1929. Related: Beeped; beeping.