Define the difference between “alarm” and “signal” in security systems.

• A. An alarm is the event requiring action due to a trigger; a signal is the notification that an event has occurred, which may trigger an alarm.
• B. An alarm is the notification that an event has occurred; a signal is the event requiring action.
• C. Alarm and signal are synonyms.
• D. A signal triggers an alarm; an alarm is the notification after action.

Answer: (A)

The difference hinges on notification versus action. A signal is the notification that an event has occurred—the data or message that something happened. An alarm is the response that requires action—the audible/visual alert or automatic escalation that prompts someone to respond.

In practice, a sensor detects something and sends a signal to the control system. If the event meets the configured criteria, the system triggers an alarm to draw attention and initiate response. A signal can exist without becoming an alarm if the event is non-critical or not rule-violating, while an alarm is specifically the action designed to prompt intervention.

Why the other views don’t fit: saying the alarm is just the notification treats the alarm as the same thing as the alert, which it isn’t—the alarm is the action/response. Saying signals and alarms are synonyms ignores that one is information (signal) and the other is an enforced response (alarm). And reverse-phrasing that a signal triggers an alarm and the alarm is the notification after action misplaces which part is the alert versus the action.