An example of alarm is Paul Revere riding through the towns to warn the people that the British were near.
An example of alarm is to sneak up behind a person and shout to scare him or her.
The dormitory doors are alarmed from 7:00 pm to 7:00 am.
A burglar alarm.
A fire alarm.
The alarm went off at 6:30.
A smoker detector is an example of an alarm.
The committee's report issued an alarm about the dangerous condition of the town's buildings.
Origin of alarm
From American Heritage Dictionary of the English Language, 5th Edition