A motion detector is a security device specifically designed to sense and quantify movement within a designated area. It employs various technologies, such as passive infrared (PIR), microwave, or ultrasonic sensors, to identify changes in the environment caused by a moving object. As described in the question, once motion is detected, the device transmits a signal to an integrated or connected system, such as an alarm panel or a surveillance system, to generate an alert. This function is a fundamental component of modern intrusion detection and physical security systems.

1. Garcia, M. L. (2008). The Design and Evaluation of Physical Protection Systems (2nd ed.). Butterworth-Heinemann (an imprint of Elsevier). p. 111, Section 6.3.1, "Motion Sensors." The text states, "Motion sensors detect motion in their field of view... When they detect motion, they send an alarm signal to the control panel."

2. U.S. General Services Administration. (2018). Facilities Standards for the Public Buildings Service (P100). Section 3.7.3.2, "Interior Intrusion Detection Systems (IDS)." This standard lists "motion sensors" as a primary component of interior IDS, which are designed to "detect an unauthorized intrusion... and annunciate an alarm."

3. Fay, J. J. (Ed.). (2007). Encyclopedia of Security Management (2nd ed.). Butterworth-Heinemann (an imprint of Elsevier). p. 581. The entry for "Motion Detection Devices" defines them as devices that "recognize changes in a particular environment," listing various types like ultrasonic, microwave, and passive infrared detectors used for triggering alarms.