All the current alarm systems consist of radars (or detectors), which are a key component of alarm systems and on which depends, to a large extent, the system's efficiency.

The radar  constitutes a small device that detects any movement within range. The detector comprises a specific mechanism ( electronic sensor ) that evaluates the amount of movement detected and then alerts the user to the presence of a moving object within the visual field.

The radar comprises a motion sensor that converts the sensed motion into an electrical signal . This is accomplished by recording changes in the optical field . The majority of radars detect any presence of up to 8-25 meters.

The number of radars which should include an alarm system depends on the size of the property.