Commercial Integrator + Security Sales Sept/Oct 2023 - 68

TECH TALK by Bob Dolph
SMARTS & PARTS
Alarm Contacts - Done Right
TOOL OF THE MONTH
IT NEVER HURTS for an alarm
professional to take a moment and drill
down into elements of an alarm system.
That's why this month I have picked one of
the most common components in an alarm
system: the alarm contact (a.k.a. window/
door sensor).
While this material will be most informative
for the newer techs to the trade,
even a good review for the old timers can be
rewarding.
Many years ago, I was employed as a senior
lab manager for National Guardian. At the
time they were the second-largest national
security company (yes, ADT was No. 1). It was
my job to review, test and recommend the
best product choices for NG.
This unique opportunity allowed me to
travel nationally and put many products
through their paces, so to speak. It allowed
me to achieve deep insight into a variety of
security system components.
If you have read this Tech Talk column
through the years, you have been exposed to much of this information,
as it has been shared with readers the past 20-plus years.
The most common, oldest and basic alarm system component
is the alarm contact.
The concept is simple. You have a magnetically biased mechanical
reed switch that changes open and closed circuit status
when a magnet is introduced in close proximity of the switch. In
the early years, the switch was not protected from the environment
and oſt en aſt er some time would begin to fail making a
good electrical contact.
The performance and reliability of the alarm contact was
considerably improved with the introduction of magnetically
biased reed switches enclosed in a small hermetically sealed
glass capsule. Still, there were some issues to consider with this
new design. Many may not be aware of these subtle performance
issues.
There is a good probability that the reed switch contacts of an
alarm sensor will remain closed and undisturbed for a long period
of time. This continuous physical contact, along with a low
supervisory electrical current can cause alarm contacts to actually
stick together, even when the door or window is opened.
This obviously would cause a missed alarm opportunity.
This is why many alarm contact manufacturers coat the reed
switch contacts with metallic compounds such as rhodium.
If you are looking for a magnetic
alarm contact series that has
broken the conventional mold,
that would be the Magnasphere.
The patented unique magnetic
ball and cup design can be
used from everything every
day to super UL high security
installations. If you are not
familiar with the product, it is
really worth a look.
When troubleshooting, a stuck contact can
be easily identifi ed by lightly tapping it to
physically open it. If you fi nd one acting like
that replace the contact.
Another word of caution for glass-enclosed
reed switches is the delicacy of the enclosure.
As a tech have you ever been installing
recessed alarm contacts in a hole that was
drilled just a little undersized? No problem.
Just give it a few fi rm taps with the heel of
your screwdriver to seat the alarm contact. I
know that I did this unwittingly in my younger
tech years.
Even with what appears to be a heavy
plastic casing, it takes less pressure than you
think to crack the inner glass enclosure. Sure,
the contact will probably work for some time.
But eventually the outside atmosphere will
make the contact act up, probably intermittently
at fi rst. Not fun.
Lightning can play havoc on alarm
contacts. When a lightning surge strikes,
the most it wants to do is fi nd the easiest
electrical path to ground. That could be going through your
alarm circuits and contacts. If this happens there is a strong
chance, even with the lightest surge, the closed normally open
(NO) contact will weld together. This will cause the contacts to
be permanently closed and would create an alarm miss if door
or window is opened.
Technically alarm contacts come in two types: normally
open and normally closed. The type of contact is described by
the nonenergized status. Since the alarm contact is energized
by the adjacent magnet to make a close alarm circuit, it is then
a NO contact.
This was so confusing to many techs that one alarm contact
manufacturer labeled its contacts NO in a NC alarm loop.
Now that we know what to watch out for in alarm contacts,
we also realize that an alarm contact can physically fail
closed for several reasons. Without regular inspections, the
only time a customer may realize this is when a window or
door is opened by a burglar and the alarm fails to update the
alarm control.
This is a great reason for adding annual inspections into your
list of services - a good extra source of RMR (recurring monthly
revenue). Some alarm contact manufacturers to consider are
George Risk Industries, Tane (my NG pick), Flair and MagnaShere
(see Tool of the Month). SSI
BOB DOLPH has served in various technical management and advisory positions in the security industry for 30+ years. To share tips and
installation questions, email Bob at bdolph.ssi@gmail.com. Access content from his 20+ years as Tech Talk columnist by going online at
securitysales.com/author/bdolph.
68 Commercial Integrator+Security Sales & Integration | Sept/Oct 2023
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Commercial Integrator + Security Sales Sept/Oct 2023

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