There are two types of motion detectors commonly used with a security system. Passive Infrared (PIR) Passive infrared (PIR) detectors are the most commonly found motion detectors and they measure changes in IR energy which is heat energy. Nearly all objects radiate energy in direct proportion to their temperature. A person with 98.6° F body temperature will radiate more energy than an object at room temperature (70%deg; F). 

The PIR detector is activated when it detects an object in its field of view that differs from the ambient temperature in the room. Most PIR motion detectors are advanced enough to automatically adjust sensitivity to compensate for changing ambient temperatures. PIR motion detectors differ in their detection pattern and range but are always made up of a number of sensitive beams. Detection occurs when an object with a different IR energy than the ambient temperature moves across an active and inactive zone in the detection area. MicroWave (MW): Sends out microwave pulses and look for a frequency (Doppler) shift due to motion in the covered area. If the radio frequency wave hits a moving object, the frequency changes and the motion detector is activated. Microwave motion detectors by themselves would cause frequent false alarms as microwave energy penetrates most building material and will therefore “see” through walls and they are vulnerable to electrical interference. Therefore, you will normally only find microwave technology used in conjunction with PIR technology and they are more expensive. Dual Technology Motion Sensors: Motion sensors can have combined features in an attempt to reduce false alarms. For example, a passive infrared (PIR) sensor could be combined with a microwave sensor. Since each operates in different areas of the spectrum, and one is passive and one is active, Dual Technology motion sensors are not as likely as other types to cause false alarms, because in order for the alarm to be triggered, both sensors have to be tripped. However, this does not mean that they never cause false alarms. Our most commonly installed motion detectors are passive infrared and are pet immune up to 55 lb. but have limited effectiveness if there are multiple pets in the room. Consult with one of our security professionals on what motion detection technology could be right for your home security needs.