Final answer:
If an alarm does not go off and an exception exists, it is most likely a system failure or a false alarm. Investigation is necessary to determine the cause and ensure safety.
Step-by-step explanation:
If an alarm does not go off and an exception exists, this would generally indicate a system failure. A normal operation would involve the alarm functioning properly, so if it does not go off, something is likely wrong with the system. However, it is important to consider the possibility of a false alarm as well, where there may not be an actual emergency. In either case, it is crucial to investigate the situation to ensure safety.