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Selecting and Installing Motion Sensors

Passive Infrared Sensors

A PIR motion sensor is good for most residential and commercial installations out to 40'. If the protection area is further away, you will need a model designed for the extended range or if available, a long-range lens for the model you have on hand.  You should always refer to the installation sheet for suitable installation locations, including height. Commonly, most detectors work well between 7.5 and 9 feet above grade. 

DO NOT INSTALL a PIR motion sensor where it will be pointed to a nearby heat source. A warm burst of air from a starting furnace or heater flowing through a colder space can easily trigger a PIR sensor. This is why you should never install a PIR sensor where it is looking directly at a heat vent or where a heat burst may be channeled to the PIR coverage area. To help overcome these issues, Multi-Tech motion sensors should be considered.  

1P or 2P?

The "P" refers to the pulse created on the sensor as infra-red energy moves between zones. A motion set for 1P appears to be more sensitive than one at 2P, however it is not more sensitive it reacts faster because the threshold for an "ALARM" condition is lower. Typically, 2P is used for pet immunity and 1P is used for maximum protection. If a 2P setting provides adequate detection, (Which you determine with a walk-test during installation) you should use the 2p setting. There are some conditions where 2P does not provide adequate protection. When located at the ends of narrow corridors such as hallways, warehouses or store isles, a 2P setting may not function as desired, even at the rated maximum distances. There may be only one or two zones covering the farthest end of the corridor. It takes at least 3 zones to use a 2P setting, A to B to A.  Place the motion in 1P mode and test for detection.  

After testing, you may determine that you cannot achieve the desired protection with the model you have. You can either relocate the sensor to increase detection, use a long-range model, or add another motion. 

Look-Down On or Off?

Look down is the ability of the motion sensor to detect motion directly beneath. If the sensor is over a door or window, then the look-down feature is OK to use. For corner location or on a flat wall, keep the look-down off. 

LED On or Off?

Some motion detectors allow you to turn off the LED. They will work during the walk test but turn off for normal use. This is a personal preference decision, but here are a few things to consider.  If the installation contains wireless motions, they always disable the LED to save power. A client may wonder why some motions have a light come on and others do not. To avoid explaining the difference, turn the LED off.
Another factor is in public spaces, someone may try to find a weakness in the coverage area by looking at the LED. Better to keep them guessing than to find a weakness in your coverage.   

PIR False Alarms

PIR Sensors do not differentiate between people, pets, birds, warm air or Mylar balloons.  Mylar balloons? yes. Mylar blocks infrared and creates a dead spot in the field of view. If close enough to the sensor, a moving Mylar balloon will create a differential between zones, not because it is a source of heat, but because it was a moving dead spot blocking ambient infrared in the room. When the balloon moves between zones it can cause a differential which results in an alarm. 

Heat vents can also create a false alarm if the motion sensor is close enough. 

Multi-Tech Motions

These sensors use microwave signals to detect the physical movement of objects in a given space. When combined with the detection of movement from the PIR part of the sensor an alarm is triggered. Multi-Tech sensors have a sensitivity adjustment for the microwave output. When set to high, these sensors can detect the movement of a mouse or sheet of paper fluttering.  Care should be taken to calibrate the microwave signal level to allow for these non-threatening movements yet high enough to detect movement at the furthest range of the required coverage area. Honeywell Dual Tec motions use yellow and green LEDs to help you determine which sensor is reacting and when red, both are triggered. 

Multi-Tech False Alarms

Multi-Tech motion sensors are not fully proof against false alarms. All it takes is a blowing mass of hot air to trip the infrared side of the detector and that same air to move a banner hanging from a ceiling, or blow a piece of paper off a desk.
Care must be taken to;

1) Identify potential heat sources.
2) What forces exist that may cause unwanted movement of loose items and,
3) Locate the sensor to minimize these effects.



In order to reduce false alarms from heat sources in the field of view of a motion sensor, some detectors provide the ability to install shields on the lens of the detector. This is known as masking. Masking does not make a detector more sensitive in un-masked areas, it only reduces the coverage area. Follow the manufacturer's manual for how to mask to achieve the desired results. 


Common Known Motion Detector Issues.

Ceiling-mounted gas heaters commonly found in warehouses and other large open spaces create a very strong burst of hot air. When their fans kick on, they can blow warm air 100’ or more. If the warm air flows high there may not be a problem, but if that air hits a beam or other reflector and bounces down into the PIR field of view, issues may arise.  That same air can cause the movement of paper, banners, and flags.  Many newer homes have the heat vents of forced air systems located in ceilings. Never locate a motion sensor close to these vents, stay as far away as you can. Ductless heat is becoming very common and if too close to a motion sensor will cause issues. These are basically like the large gas heaters in warehouses, but smaller and in small rooms. Their heat bloom is smaller due to their heat source, but the fans can be strong and they can oscillate.

Ceiling fans can play havoc with a microwave signal.  Commercial buildings may not have fans running during installation. In some cases, you may not even notice them. Days, weeks or a month later the fan can cause higher warm air to move down into the motions field of view and move a flag, banner, paper, or a rat runs across the floor, I have seen that on video.  A fan can also keep the motions micro-wave sensor tripped, so only a heat movement is required to trip the detector.  Always keep an eye out for fans or other items that a customer may leave on, which can trip the micro-wave motion sensor part of a Duel-Tec motion detector. 

All electronics are affected by temperature, motion sensors are very sensitive to heat and cold. If located in an unheated space you will need to verify the motion you are installing is temperature-compensating. Not all are and a very cold night can result in false alarms.

The width of the PIR sensor zones starts off very small and grows wider as you move further away from the sensor. For this reason, a small bird flying up close to a PIR sensor can trip the sensor whereas the same bird flying further away will not.

Rule number 1 in motion sensor false alarm prevention - The larger the area, the more potential false alarm triggers exist. You cannot catch them all, but with a little observation and logical thinking, you can avoid many of them.