Grouping Sensors in Zones

Sensors can be grouped into zones. For example, a zone labeled “reception area” might include the magnetic switch on the public entry door, one or more passive infrared sensors in the reception area, and glass-breakage sensors for the reception-area glass. If one or more of the sensors is tripped, the alarm monitoring panel or central station might display “Reception Area.”

Grouping sensors into zones has the advantage of reducing the cost required to link each individual sensor to the alarm processor on its own cable. It also allows the use of an alarm processor that handles fewer zones (sensors), reducing the cost of the processor.

Grouping sensors has disadvantages. If one sensor malfunctions, generating a trouble or tamper alarm, each sensor in the zone must be examined. Another disadvantage is that if one sensor malfunctions, the entire zone may have to be disabled until the malfunctioning sensor can be located and repaired (or at least disconnected from the zone).

For rapid and precise response to alarms, it would be best to have each individual sensor uniquely identified at the alarm monitoring location. This would enable the alarm monitoring officer or company to tell the responder exactly which door was opened, which window was broken, or which area’s volumetric-motion sensor was tripped. Additionally, such a system would enable the monitoring party to “track” the movement of an intruder by observing subsequent sensor activations. Multiple sensor activations can allow someone monitoring the alarm to determine an intruder’s probable location in the facility and relay that information to security responders.

Some alarm systems have audio monitoring as an option. One or more microphones are installed in the facility and wired into an audio module in the alarm processor. If an alarm occurs, the microphones pick up sounds inside the facility and transmit them over the link to the alarm monitoring location. Someone monitoring the alarm can listen to the sounds to help determine the cause of the alarm. The Forest Service would need to weigh the value of this feature against the issue of illegal nonconsensual audio surveillance if the system inadvertently transmitted conversations between persons authorized to be in the area who have a reasonable expectation of privacy.