A motion sensor alarm is a device that uses optical, microwave, or acoustic sensor technologies to detect motion around your home or workspace; and to let you know that there is a physical security event that shouldn’t be happening. Motion sensors are also sometimes known as motion detectors.

A complete motion sensor alarm system has a few main components. The first is a motion detector, which is the most outwardly evident part of it (that’s why the whole motion sensor alarm system is sometimes only known as motion detector). This motion detector is generally a passive infrared sensor, and is just a generally white block with a semi-translucent panel that receives IR radiation, and detects changes over time.