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Motion Sensors-Passive Infra Red

Motion Detectors-Ultra Sonic

Motion Detectors-Microwave

Dual Technology Motion Detectors

Motion detectors - Photo Beams


Home Security 101

Motion Detectors

Just as a starting note: All most every object, will emit or reflect some level of Infra Red Light (Heat)

Here again, there are several types available, as well as several manufactures of these detection devices. Each compelling you to believe that their device is better than their competition. The cheaper models of motion detectors are those of what's called Passive Infra Red. There is a lot of different types of even these sensors. There's single pulse, multiple pulse, different frequencies,  different filters...etc. It all can be very confusing. The common thing to know about Passive Infra Red motion sensors is that they all operate along the same basic parameters. 1st, They emit no light source, 2nd, they all use what's called a Fresnel lens. This is a lens that focus's the Infra Red spectrum of light from a broad range, typically in residential applications the range is 35 to 50 feet in length, to an area on the sensor that's about 1/4 of an inch square. The lens does this in a manor that fingers in the incoming Infra Red light. The example below is of a model that will cover a 20ft wide 35ft length.

Motion Sensors-Passive Infra Red

In most residential applications these, along with most all wall mounted motion sensors, are mounted at a height of between 5ft and 10ft from the floor. The overall mounting height of the sensor has an effect on its operational range in distance. (See the above illustration, Side View) At approximately 5.5 feet mounting height, the distance range of coverage is 35 feet in length.
     These "Fingers" are to detect the presence of Infra Red light emitted, radiated or reflected by any object. By focusing the incoming light into smaller areas, this allows for the "motion detection". Any object that emits, radiates or reflects any of the infra red light spectrum and that pass's through 2 or more of these "fingers", trips the sensor. By doing the sensing in this fashion, objects that may be in the "Line of site" of the sensor, that may radiate or reflect heat (Infra Red Light) due to direct sunlight or other heating sources, are less likely to trip the sensor. As you might imagine this has an effect on the placement mounting of this type sensor. Infra Red Sensors are exceptionally sensitive to ambient sunlight, environmental ambient air temperatures and any variances of these temperatures. Direct sunlight, in most cases, will cause this sensor to activate, so mounting these sensors in direct sunlight is not advisable.

Generally, for the infra red  motion sensor to activate an object must be in motion. As it enters the sensing area, the sensor starts "watching it" (for a simpler description)


Depending on the objects speed, the Motion Detector will stay activated as long as the objects in the field of view and is with in any 2 finger coverage areas. It is possible to stop and the detector will reset, but again, if any moving object is with in any 2 finger coverage areas the detector will activate.  There are models available that claim to be Pet tolerant up to 100 pounds. But, there are always problems.

Infra Red motion detectors have there applications in home security. It is not advisable to use infra red detectors alone as intrusion devices. Because of their extreme sensitivity to ambient light and air temperature they are prone to "False Alarms" or false activations. They have multiple applications as annunciation activators (like door bells), Exterior or Interior security lighting or even to activate a locking device on an entry/exit door.


Motion Detectors-Ultra Sonic

We won't dwell on this type sensor very long. It is out dated and very unstable.

But just as a reference note in your search for a motion sensor, if you run across one of these:

        Ultra Sonic sensors also have varying ranges in their field of coverage and, they too, come in many varied manufactured looks or styles.
        But because of their component makeup they are Extremely Ambient Air Temperature Sensitive. They require a very temperature stable environment. They function very similarly to Radar. Using a piseo electric diaphragm for the units transmitter and a receiver. These elements will vary in rigidness and flexibility depending on their physical temperature this can cause false readings in the pulse width and return time.
        Operationally, the transmitter sends out a pulse at a frequency just outside the audible range(Ultra Sonic) somewhere above 30 thousand cycles per second (30Khz). The unit then counts the time that it takes for that pulse to return to the receiver. Depending on the sensitivity setting of the unit, if the signal transmitted returns faster than the receiver expects it to return, the unit activates.
        Ultra Sonics applications are better left to distance and range finding. Not a good Idea to use one of these in a home security application.

Motion Detectors-Microwave

Before we begin this sensor, it needs to be stated that the microwave energy that the motion sensors utilize is in no way harmful. Your exposed to more microwave energy sitting in sun during the day than any where near what these sensors emit. Microwave energy is only harmful at direct high exposure levels, Several watts. Most every one has passed through an automatic door, at grocery stores, airports...etc. The little Black Boxes mounted above the door frame, 98% of the time is a Microwave Motion Detector.

Now here were talking serious true motion detection. The same applies to Microwave detectors as all others discussed to this point, in as it applies to styles and manufactured looks or packages. Microwave operates at a very high frequency. Microwave operates very similarly to ultra-sonics. In as much as it is a range or distance finder. But because of its high frequency and component makeup it is super stable when compared to ultra sonics. Microwave uses a tuned antenna for transmission and reception of it's signals. We're not going to get into the details of wavelengths and there effects at higher and lower frequencies. Suffice it to say that microwave energy can penetrate walls.

Here's a quick example of the two different coverage areas of Microwave and Infra Red detectors

As you can see, the Microwave coverage penetrates the wall, the Infra Red only pass's through the door way. Both provide coverage, Both have advantages and disadvantages. 

Microwave has advantages over Infra Red and Ultra Sonics. One of which is that it's not temperature sensitive. Most can even be set up as a directional detection device. This simply means that it can detect motion moving towards or away from the detector selectively or both moving towards and away. The technology used to do this is called the Doppler effect. Microwave technology, despite the advances and stability still have drawbacks.
        Example; imagine the problems that occur in a commercial application if there were 2 adjacent business's in a strip mall. #1 didn't close for business until 2 or 3 hours after #2.  #2 has a microwave motion detector looking at an adjoining wall and the security system has been Activated, armed or turned on (depending on your description). If the microwave were to penetrate the wall to see activity in #1, #2 business's alarm would "False Alarm". No one's actually trying to break in, the detector just saw motion through the wall from business #1. Extreme but possible.
        In home security applications a microwave sensor alone is too sensitive for most residential use as far as using it for intrusion detection. Needless to say microwave, because of sensitivity reasons, is not very pet tolerant. Microwave detectors should be mainly used for annunciation, door actuation, lock/unlock and lighting mechanisms.

Dual Technology Motion Detectors

Ok, we now have been though the basic operation of most the wall mountable motion detectors available on the market today that might have application in residential security systems. You might have noticed, in each section, none of the individual sensors would be a consistently reliable form intrusion detection. Then why, you might ask, have they been included in this information? To give you better insight when looking for security devices. With a little understanding of the devices you can make your system more reliable. The problems with these individual detection devices has been know for a long time. Manufactures of each device have respectively bettered their technology, but their all still prone to false activations. Technology today for motion detection has been greatly improved and stabilized by combining the technologies into one unit.
       The most effective and reliable motion detectors available on the market today utilize dual technologies. Most manufactures use the Infra red and Microwave technologies together. Some have attempted Infra Red and Ultra Sonics, But they have not been proven to be consistently reliably stable.
       By using a Microwave and Infra Red combination you get the benefits of heat detection or presence, and the true Doppler motion detection of a microwave. Both the Infra Red (sensing heat variations in physical motion) and the Microwave (Which is not light or temperature sensitive, sensing any object in motion) must be activated simultaneously before the unit will activate. This greatly reduces the false activations or " false alarms"   

 Because of the dual Technologies, it's not as critical but all ways more effective if you can mount a motion sensor where the intrusion motion would be across the covered field as apposed to directly toward or "Face On" with the intrusion motion. See examples below.

 In this example, the intruder is traveling towards the detection device. Because of  the infra red fingering the intruder would travel approximately ten steps  in to the coverage field before detection. This doesn't sound like much but Time is your critical problem here. Ten steps closer to your valuables before detection. The average time a burglar has in your home is less than 1 minute. The average dispatch time and response by law enforcement is 3 to 5 minutes.  Earlier detection means better chances to catch the intruder.




In this example, you can see that the intruder has all ready entered the Microwave field of coverage and in approximately 1 to 2 steps he will be in the Infra Red field of coverage. As you can see, this application will activate the motion sensor  faster.



The above motion detector application would also apply if you were to use just a single technology motion sensor such as a passive infra red.  Although not as reliable as dual technology motion detectors, infra red motion detectors are somewhat less expensive and will provide reasonable coverage. Most states law enforcement have enacted False Alarm ordinances and fine the home owner if too many false alarms occur in a short period of time. In some areas these fines can reach as much as  $250.00 per occurrence and some states only give you 2 false alarms before they enact the fines. So spending the extra $5-10 (Average cost difference)  on a dual technology motion detector is a wise investment.


Motion detectors - Photo Beams

There are various other types of motion detectors. Most all of what we have discussed up to this point have been wall the mounted type. There are ceiling mount type in both Passive Infra Red (PIR) and dual technology Microwave and PIR. The only real difference in their operation is that they are not as directional per-say. Because they are mounted on the ceiling, they are manufactured to see motion in 360 degrees. The average coverage area is about 50 feet in diameter.

Photo Beams come in many different types of configurations. Although a lot of distributors consider photo beams, motion detectors, that's not really what they are. Most all Photo Beams are PIR in nature. But they do not have the Frenell Len's. Instead they use conventional concave lens's and light filters to focus and amplify the light. I said that photo beams weren't actually motion detectors, there not. They're Presence sensors. Photo Beams only activate when there single beam is broken or reflected, depending on the type. As long as you stand with in the beam, the sensor stays activated. This is not the case with motion detectors, if you were to stand still in a motion detectors field of coverage you would see it reset until you began to move again. So, you can see the difference between Motion detectors and Presence detectors.

To start, we will look at what's commonly called a "Through Beam" photo beam. It is called this because it requires 2 main parts. A transmitter and a receiver. This configuration creates a through beam of infrared light. Any object that breaks this beam activates the sensor. This beam is invisible to the naked eye and contrary to movies, you can't blow smoke and see the light beam. Although, you can see the beam using a Black and White camera and a little smoke, if you want to do a little experimenting.

Another common type is the "Reflective" photo beam. These types are generally smaller packages. They also require 2 components. 1 the transceiver unit and a retro-reflector, similar to a bicycle reflector. The transmitter--transmits the light, the reflector--reflects it back to the receiver. Here again, if the beam is broken, the sensor activates. These particular types are used in many stores at the front doors to sound a chime upon entry to the store.

A variation to the reflective photo beam is a more aptly used type in home security. It operates basically the same as the above type but with out the retro-reflector. It uses any object that comes with in the range of the detector, your the reflector. In this case, the sensor is not activated until you walk in front of it, it reflects the light off of you back to the receiver. These type units come in a package about the size of a single gang electrical box. (Approximately 2.5 inches wide, 3.5 inches tall and about 2.5 to 3 inches deep) They are mounted in about the same place that you would find an electrical outlet for camouflage and the units even come with electrical outlet receptacle looking covers. Standing in a room full of electrical receptacles it's hard to tell the difference. 

As you can see, Photo beams are not really motion detectors per-say, their more presence detectors. They are limited in there applications. We will get into more of the different applications for all the different devices later in this research.

 We will stop in this area with this last little bit of thought application. There are devices available on the  market to day that claim Pet Immunity. Claiming that the detector will ignore pets, some up to 100 pounds on average. Remembering here that we have been talking about motion detectors. Some of these devices actually work fairly decent, IF they are applied correctly. Most of the "Pet Immune" devices raise the floor of coverage. In other words the coverage of the motion detector doesn't start for some 2 to 3 feet off of the floor. This allows for animals to roam with out triggering the Motion detector. The ideal conditions for motion detection coverage is to remove or not allow entrance by anything to the area that's to be covered by motion detection. But in most cases this is not a practical possibility. Most of these devices will offer adequate coverage by keeping a few basic thoughts in application and placement in mind.

Consider, any areas that might be an easy access into the field of coverage. Placing couches, chairs, large shelving, tables….anything that may allow an animal to gain inadvertent access into the field of coverage of the motion detector. In most applications, it is possible to provide coverage in a cross the room coverage with out this problem occurring. Just look around and be aware of the possibilities. By doing this small pre-thought in the installation, it will make the system more reliable and less False Alarm prone.

Here again, natural building structures in your house can also cause this false alarm problem. In the right application of the stairwell,  this motion should have been concerned with not so much the stairwell but access to the stairwell. Or not looking directly at the stairwell it self but the area around it that provided the access to it, Not to mention, that by protecting the access, normally, you provide coverage to a larger area.

We will get into more detail in placement and applications later.

  Security Applications.

We all know that the times ahead are only going to worsen.

It's not a question of

 "will I need",

but what do I need to adequately protect my family, property and investments.

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