Just as a
starting note: All most every object, will emit or
reflect some level of Infra Red Light (Heat)
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
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
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
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
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.
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.
We won't dwell on this type
sensor very long. It is out dated and very
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
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.
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
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
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
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
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
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
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
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
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.
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
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.
detectors - Photo Beams
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.
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
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.
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.
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
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.
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.
areas that might be an easy access into the field
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.
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