Subscriber Discussion

Alarm Contacts Tutorial

Ari Erenthal

•Feb 20, 2017

Contacts are the devices that tell an alarm panel when an entryway, such as a door or window, is open or closed. The act of opening or closing an entryway causes a physical change in the contact, whic...

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Paul Curran

•Mar 07, 2017

In the U.K. Anti mask contacts consist of two reeds (for U.K. Grade 3 and above).

There are two reeds, so if you put a magnetic on the contact or you try to fool the contact with a magnetic it pulls the wrong reed and generates a "mask" condition. For this reason there is a finite gap which needs to be adhered to. This change is signalled via EOL.

Im unsure if the same is true in the US?

I guess this is similar to Magnasphere.

The same is true for flush mount or roller door contacts. Interestingly if the distance on the roller door is too large you must fit one at each end so you can't jack the door up and slide under.

If the door is high security its advised to fit one at the top and one at the bottom on the side ( or other combinations) why? They cut the bottom of the door and open the bottom section leaving the top contact closed! A more common practice is to also fit a PIR or dual technology (microwave and PIR) sensor behind the door.

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Ari Erenthal

•Mar 07, 2017

In reply to Paul Curran

What you call anti mask, we call "biased". From your description, it seems like we're talking about the same thing. Magnasphere is a particular implementation that uses a ball bearing which detects any attempt at defeating the switch.

If the door is high security its advised to fit one at the top and one at the bottom on the side ( or other combinations) why? They cut the bottom of the door and open the bottom section leaving the top contact closed!

Seen this, too, especially for roll-down gates. That's why I prefer bottom mounted contacts to rail contacts.

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Paul Curran

•Mar 07, 2017

In reply to Ari Erenthal

Yes I think it's one and the same bias / anti mask. Here it's a standards issue- the insurance companies demand it and therefore the Police and security inspectors. :)

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Undisclosed Integrator #1

•Mar 08, 2017

Thank you for this article. While I don't deal with alarm related items often when it does come up it has been a crash course in proper device selection. This assists greatly.

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Daniel Filomena

•Mar 08, 2017

IPVMU Certified

Just wanted to note - there are Steel Door "push-in" door contacts with larger magnets that last a while longer than wooden door type. I like to make sure metal shavings are not there to collect on magnet as it sits for years.

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