What should a sentry do if they witness a fire or disorder?

The correct action for a sentry who witnesses a fire or disorder is to give the alarm. This immediate response is critical because it ensures that the necessary personnel are alerted to the situation as quickly as possible, allowing them to take appropriate action to mitigate the threat and protect personnel and property. A timely alarm can prevent further escalation of the situation and facilitate an organized response from emergency services or other military units.

In high-stakes environments, particularly within a military context, the responsibility of a sentry involves not only maintaining security but also ensuring safety. By sounding the alarm, the sentry fulfills their duty to respond proactively to emergencies, making this choice the most appropriate response.