If something alarms you, it makes you afraid or anxious that something unpleasant or dangerous might happen. We could not see what had alarmed him. = frighten
Alarm is a feeling of fear or anxiety that something unpleasant or dangerous might happen. The news was greeted with alarm by MPs
An alarm is the same as an alarm clock. see also alarming, alarmed, burglar alarm, car alarm, false alarm, fire alarm, smoke alarm
a device that signals the occurrence of some undesirable event an automatic signal (usually a sound) warning of danger fear resulting from the awareness of danger warn or arouse to a sense of danger or call to a state of preparedness; "The empty house alarmed him"; "We alerted the new neighbors to the high rate of burglaries