What does an Intrusion Detection System (IDS) detect?

• A. A change in state of detection devices that may require further investigation
• B. A hardware failure
• C. A weather change
• D. A user login event

Answer: (A)

An intrusion detection system is focused on sensing changes in security inputs that may signal a potential intrusion and then alerting for investigation. It looks for events like a door sensor being opened or a motion detector firing, which represent a shift from normal to alarm state and warrant further checking. This is why detecting a change in the state of detection devices is the best match. Hardware failures, weather changes, and routine user login events fall outside the core role of a typical IDS in physical security: hardware faults are handled by fault management, weather isn’t a security input the IDS processes, and a user login event aligns more with cyber or access-control logs than with physical intrusion sensing.