alarm (n.)
early 14c., from Old French alarme (14c.), from Italian all'arme "to arms!" (literally "to the arms"). An interjection that came to be used as the word for the call or warning (compare alert). Extended 16c. to "any sound to warn of danger or to arouse." Weakened sense of "apprehension, unease" is from 1833. Variant alarum is due to the rolling -r- in the vocalized form. Sometimes in early years anglicized as all-arm. Alarm clock is attested from 1690s (as A Larum clock).
alarm (v.)
1580s, from alarm (n.). Related: Alarmed; alarming.