Which sensor types are commonly used for intrusion detection?

• A. Door/window contacts and motion detectors (PIR)
• B. Smoke detectors
• C. Temperature sensors
• D. CO detectors

Answer: (A)

Intrusion detection relies on sensors that alert when entry occurs or movement is detected. Door and window contacts are a staple because they monitor every opening point; when a door or window that should be closed is opened while the system is armed, the switch is triggered and an alarm is raised. Inside, motion detectors, especially passive infrared (PIR) ones, watch for moving bodies in a room by sensing heat energy. Together, they cover both perimeter and interior monitoring, making them a core pairing for detecting unauthorized entry.

Smoke detectors, temperature sensors, and CO detectors serve fire safety and environmental monitoring. While they’re valuable for overall safety and may be integrated with a security system, they aren’t designed to detect intrusions, so they aren’t the primary choices for intrusion detection.