What type of sensors are primarily used in detecting motion in security systems?

Passive Infrared (PIR) sensors are primarily used in detecting motion in security systems because they are designed to detect changes in infrared radiation, which is emitted by objects based on their temperature. When a warm body, such as a person or animal, moves within the range of the sensor, it causes a change in the infrared levels detected by the sensor. This characteristic makes PIR sensors highly effective for motion detection, especially in indoor environments like homes and offices.

PIR sensors are widely favored in security systems due to their reliability, cost-effectiveness, and low power consumption. They have a broad field of view and can effectively cover large areas with minimal false alarms when installed correctly. The way they work is influenced by the natural thermal patterns in the environment, allowing them to distinguish between moving objects and the stable background.

Other sensor types, while used for various applications, do not serve the primary function of motion detection as effectively as PIR sensors do. For instance, magnetic sensors are typically employed in entry points like doors and windows to detect when they open. Ultrasonic sensors can detect movement but are more suitable for specific applications and environments. Photoelectric sensors are often used for distance measurements and object detection rather than real-time motion sensing in security contexts.