Which of the following best describes a motion sensor used in access control?

A motion sensor in access control systems is designed to detect movement within a specified area. When movement is detected, the sensor can trigger various actions related to access control, such as unlocking a door, activating an alarm, or alerting security personnel. This functionality is key for enhancing security and enabling automated responses to potential intrusions or authorized entries.

The focus of a motion sensor is on detection rather than identity verification, recording, or maintaining lock engagement. Therefore, its primary role revolves around the ability to sense and respond to movement, making it an integral component of modern access control systems that require real-time awareness of physical spaces. This is why the correct description highlights its role as a tool that detects movement for triggering actions within the access control framework.