Re: Help with 7 Circuit Project?

["Robert L Bass" <robertlbass@xxxxxxxxxxx>]

> My only concern is discussing your ideas about
> how to make the system reduce false alarms...

There are several things you can do to reduce the likelihood of false
alarms.  Selection, placement and programming of motion detectors should be
at or close to the top of your list.  If there will be free roaming pets in
the home while the system is armed, the detectors need to be "pet resistant"
type.  These employ various schemes to differentiate between 2- and 4-legged
targets.

The simplest "pet proof" detectors are aimed across the protected space at a
level above the height of one's pets.  This may work with some dogs but cats
can jump from the floor to the top of a refrigerator.  Another sensor type
uses a split transducer to pick up IR (body heat) from an intruder.  The
split transducer receives IR from low and high level objects.  A processor
looks for motion in both upper and lower areas at the same time.  If the
motion is only along the floor or on top of the couch nothing happens.  If
there is simultaneous activity from both planes the detector throws a relay
and the alarm system is triggered.  There are other types of pet resistant
technology but this is the most common method.

Dual technology detectors have microwave and passive infrared (PIR) sensors
in the same housing.  The alarm is not activated unless both sensors are
triggered together.  Because the detectors respond to different stimuli,
there is lower risk of a false from a dual tech sensor than a single
technology device.

As mentioned above, placement is an important aspect of false alarm
prevention.  During takeovers of competitors installations I've found
countless instances where single tech PIR motion detectors were installed on
inside walls facing directly at windows.  This can be a major source of
problems.  PIRs will often trip if sunlight, car headlights or any other
strong source of IR light is momentarily reflected through a window onto the
surface of the detector.  Many detectors' installation instructions clearly
state that they should not face a window.  Unfortunately, because interior
walls are usually uninsulated, lazy (or poorly trained) techs like to place
them there.  A little extra effort is required to place the sensor where it
belongs but the effort will be rewarded with better performance.

Among the useful tools for reducing false alarms are certain control panel
programming options.  Interior detectors in the path from the entry door to
the alarm keypad should be programmed as "interior follower" zones.  This
will allow the homeowner to pass the detector during the exit delay after
arming the system without triggering an alarm.  It will likewise allow you
to pass the detector after entering a delay zone (usually the door) upon
return.  However, if the detector is triggered before the entry door is
opened the alarm is activated immediately.

Another false alarm reduction technigue that is available with some systems
is called "zone ANDing".  Two or more zones (sensing loops) are grouped
together within an AND group.  The alarm will only sound if at least two
zones are tripped within a given time frame.  Some panels, such as the Napco
Gemini series, can be programmed to sound the siren on the first zone
tripped but will only send a signal to the monitoring center after a second
zone is tripped.

There is much more to false alarm reduction but the above are a few things
you should consider when planning an installation.

> I am not worried about being sued, but if I discuss
> this topic in depth, I would feel terrible if someone
> who did not grasp security and programming and
> tried to change the way HAI does security, and
> something tragic happened.

I disagree.  False alarm reduction techniques should be Course 101 for every
user, installer, DIYer and service person who uses or works on an alarm
system.  The real tragedy of the security industry is the 98%+ ratio of
false alarms which have caused police departments across the country to
consider alarms and the alarm industry a public nuisance.  Because so many
alarms are a waste of time, police departments sometimes respond slowly or
not at all to real alarm conditions.  There is a far greater risk of tragey
in this situation than arises from attempts to educate DIYers on the
subject.

--

Regards,
Robert L Bass

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