Have you ever read a sign saying ‘THIS DOOR IS ALARMED” and wonder at how a door could be so scared?
Alarme! Alarme! was a Medieval cry meaning ‘to arms’ coming to English from Old French and Italian, from the Latin ad illas armas.
The shout was often accompanied by a clanging bell or loud horn and the meaning of the exclamation moved to describe these sounds.
The meaning has further shifted to also describe the feeling people have when there is imminent danger.
An alarm clock is obviously heralding the danger of the new working day.