Home Security System | Types Of Motion Detectors For Alarm Systems

How Microwave Sensors Work:

Microwave sensors bounce microwaves off of an object, then measure the frequency of the returning waves. If the particular object is moving, it will send back microwaves of a differing frequency. Microwave sensors can offer a greater range of coverage than infrared sensors, and are more reliable at greater distances. Microwaves can also penetrate walls, which means that microwave sensors can be placed behind objects. The only negative aspect of these types of sensors is their strong sensitivity, and the fact that they are vulnerable to interference from other electrical devices such as lightning, or radios. Luckily, your installer can adjust the sensitivity of your microwave sensors quite easily to work best in your particular environment.

Types Of Motion Sensors And Their Effectiveness:

Above: Coverage Area For A Dual PIR (Passive Infrared) Motion Sensor (Click For Larger View).

How Infrared Sensors Work:

The most common type of sensor seen mostly in home installation is the infrared sensor, as it tends to be cheaper and more reliable than microwave sensors. This type of sensor utilizes the infrared light spectrum, which is an invisible light that emanates from any heat source. The sensor measures the heat of any object that passes by it, and compares this heat to a background setting, such as a wall. One of the drawbacks of infrared sensors though, is that they don't actually cover a full room. It covers a scanned area, kind of like fingers pointing out into the coverage area. The area between the fingers are not covered (except in the example shown, which uses dual pir technology). The plus side though, is that different lenses can be used, depending on the environment the sensor is in. For example, a long hallway can use a lower angle lense (appr 30 degrees) that covers a greater distance.

Some motion sensors use a combination of these features to improve its reliability. These are called "dual technology" sensors, or "dual tech" sensors. These are becoming increasingly popular, as they greatly reduce false alarms by combining the penetration capabilities of microwaves, and the heat sensing properties of infrared. Any motion or heat sensing device can have its sensitivity adjusted by your installer.

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Above: Motion sensors also come in ceiling mounted models, great for rooms with office cubicles.

Learn About "Pet Immune" Motion Detectors

Motion sensors detect any movement in areas covered by that particular device. Some detectors use microwave sensors to detect movement, others use infrared sensors.