Definition of alarm:
a summons to arms, as on the approach of an enemy; any sound or information intended to give notice of approaching danger; a warning sound to arouse attention; a warning of danger
"arming to answer in a night alarm. --Shak."
to call to arms for defense; to give notice to (any one) of approaching danger; to rouse to vigilance and action; to put on the alert; to keep in excitement; to disturb