Which of the following is NOT a commonly used intrusion sensor?

A smoke detector is designed specifically to detect smoke and fire hazards rather than unauthorized intrusions. While it is a critical component of safety systems, its primary function is to alert occupants of smoke or fire rather than to monitor for someone entering a restricted area.

In contrast, intrusion sensors such as glass-break sensors and magnetic contact sensors are explicitly intended to detect unauthorized access or breaches in security. Glass-break sensors detect the sound frequency of breaking glass, while magnetic contact sensors are used on doors and windows to trigger an alarm when the contact points are separated. Duress alarm codes also play a role in intrusion detection by allowing individuals to signal for help discreetly when they are threatened or coerced.

The other options are all tools that contribute directly to the detection of intrusions, making a smoke detector the clear choice for something that is not categorized as a common intrusion sensor.