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SYSTEM OVERVIEW
INTRUSION DETECTION SYSTEMS
Alarm monitoring for intrusion detection is an integral part of any access control system.
Not all doors will have access or egress control devices.
On doors that permit access to the facility but do not need access or egress control, door status switches (a.k.a. DSS, alarm contacts, door monitors) or similar detection devices are required at all perimeter portals.
A door status switch monitors the status of a movable barricade or door.
DSS are also used on window openings to determine if a window is opened or closed.
DSS are made in many sizes, shapes and styles and the appropriate alarm contact for a particular portal is relative to the style of door or window being protected.
For instance, in cases where cosmetics are an issue “button contacts” are generally used.
BUTTON CONTACTS
A button contact consists of two components, a small magnet that is inserted in a window leaf and a corresponding sensor inserted in a window frame.
The sensor is wired to the alarm monitoring panel and provides a signal when the window is opened.
When the door or window is closed, the magnet is in close proximity to the sensor and holds a “read switch” closed.
When the door or window is opened, the magnet is moved away from the sensor and the read switch opens.
It is this action of opened/closed which gives the alarm contact its signaling capability.
NORMALLY OPENED VS NORMALLY CLOSED
In some cases, DSS are Normally Opened while in other cases these contacts are Normally Closed.
The selection of Normally Opened verses Normally Closed alarm contacts is predicated upon the type of alarm system you are using.
The manufacturer of the alarm monitoring system will define which type of contact is appropriate for the system.
In most cases, Normally Closed contacts are required.
In surface mounted DSS applications, the alarm contact will again consist of two components and will be wired from the doorframe to the corresponding alarm system. These devices are usually mounted to the inside surface of the door in close proximity to one another. When planning the use of surface mounted DSS, it is best to place the contact as far away from the door hinge as possible. This will mean that the smallest movement in the door will be perceived by the DSS and is less likely to be defeated.
Most all DSS work in this manner and the selection of the appropriate contact can be made by studying the application manuals from the alarm contact manufacturers. The astute security professional will have a thorough understanding of which contacts are most appropriate in which circumstance and will select the appropriate contact for the portal.
In surface mounted DSS applications, the alarm contact will again consist of two components and will be wired from the doorframe to the corresponding alarm system. These devices are usually mounted to the inside surface of the door in close proximity to one another. When planning the use of surface mounted DSS, it is best to place the contact as far away from the door hinge as possible. This will mean that the smallest movement in the door will be perceived by the DSS and is less likely to be defeated.
Most all DSS work in this manner and the selection of the appropriate contact can be made by studying the application manuals from the alarm contact manufacturers. The astute security professional will have a thorough understanding of which contacts are most appropriate in which circumstance and will select the appropriate contact for the portal.
DOOR STATUS SWITCHES AS ALARM SYSTEMS
DSS is also used for access control doors to provide an alarm if the door is opened improperly.
These DSS switches are generally used in conjunction with the electronic controls of the access control system.
The system is designed to “shunt” or turn off the alarm with the access control system receives an indication that the door is being opened legitimately such as when an authorized card is used to gain access or a proper request to exit is registered with the system.
Care should be taken to monitor every opening in a secure perimeter when planning an access control / alarm monitoring system.
Care should be taken to monitor every opening in a secure perimeter when planning an access control / alarm monitoring system.
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