3.0—Home Security and Surveillance Systems

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Chapter
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3
Motion Detectors
Motion detectors work by detecting the changes in the infrared energy in
an area. Because these devices do not emit any energy, they are called
passive infrared (PIR) detectors. PIR detectors use a lens mechanism in the
sensor housing to detect a change in infrared energy across the horizontal
sectors covered by the sensor. This type of detector is insensitive to stationary
objects but reacts to rapid changes that occur laterally across the
field of view. They are the most common and economical type of motion
detectors and are available in standard, pet-friendly, and harsh-environment
(outdoor) models. An example of a motion detector for interior use is
shown in Figure 3.4.
Figure 3.4 Motion detector.
Security Panels
Security panels provide several functions to coordinate the operation and
management of a security system. They can include an integrated keypad or
LED indicators. Most designs include a power transformer for converting
the AC voltage to a DC voltage for the sensor loop and contain a rechargeable
battery for backup if the commercial power fails. A terminal strip provides
for the connection of the wiring that connects all the sensors to the
controller as well as the external telephone line. Most designs include a
printed circuit board containing all the electronics and a microprocessor. It
also connects to and controls the siren that is activated when an alarm condition
exists.
Security panels are known by numerous names, such as central control box, control panel,
alarm panel, and interface panel. They all perform similar functions including controlling and
monitoring sensor status, providing power to the system, connecting the telephone line to the
monitoring station, and handling the programmable options for the system.