threshold. As a result, the sensor can distinguish between movements of both
small objects (such as birds) and the larger motions of humans. The pattern
should be set up in an area with stable surfaces avoiding objects whose
surfaces can vibrate.
Microwave. This sensor is a transceiver which transmits and
receives a radar frequency wave pattern. The sensor detects changes in the
wave pattern generated by movements and results in alarms. The wave pattern
will penetrate glass, masonry walls, and other nonmetallic barriers so that
the sensor should not be aimed at an outside wall. Sources of nuisance
alarms, such as wind-caused movement of metal objects, should be avoided.
Passive Infrared. Passive infrared sensors respond to the
energy emitted by the human intruder, which is comparable to the heat
radiated by a 50-watt light bulb. As infrared energy does not penetrate most
building materials, sources located exterior to the facility will not
typically generate false alarms. However, local heating effects can lead to
false alarms via sunlight through windows. Such geometries should be avoided
during sensor placement.
Sonic sensors. Sonic sensors can be active or passive.
Passive systems in their simplest forms use a microphone and an amplifier to
detect sounds generated by an intruder. Active sensors are equivalent to
ultrasonic sensors operating at audio frequencies. They detect the Doppler
frequencies generated by intruder motion.
Capacitance proximity sensor. This interior sensor is used to
detect intrusions to metal objects. The sensor detects changes in
capacitance between the protected object and ground that are caused by the
approach of an intruder. The alarm relay is activated in a fail-safe
configuration so that an intruder, loss of power, or breaking of the
protection loop will cause an alarm.
Duress Switches. Duress switches activate remotely located alarms.
They are typically placed in hidden locations and activated by guards or
Closed-Circuit Television (CCTV)
Introduction. The same CCTV technology discussed under exterior
site security (par. 4.6) can also be applied for threat assessment and
surveillance on building exteriors or within building interiors. The
following briefly describes its application to the building. The reader is
referred to par. 4.6 for a summary of the technology. Sources of more
detailed design information include: