Microwave sensors are not affected by air turbulence.
c) Microwave sensors may interfere with and be interfered by the
operation of computers and other electronic equipment.
a) Fluorescent lighting is an ionized column of gas which reflects
microwaves and can appear as a moving target to this type of sensor.
Turning off the lighting when the alarm system is in use can reduce this
problem, but also reduces remote visual assessment capabilities.
b) Wind-caused movement of as little as 0.25 inch by large metal
objects such as overhead doors can cause nuisance alarms. Positioning the
sensor pattern to parallel such nuisance stimuli will reduce nuisance
c) Potential sources of nuisance alarms such as moving ventilation
fan blades can be masked by metal screening.
d) In general, the structure barrier penetration problems and
other electronic interference problems limit the use of these sensors in
interior DoD applications due to the likelihood of nuisance alarms.
4.2.4 Audio Sensors. These sensors, also called "sound" sensors, consist
of one or more microphones connected to an electronic analyser. Ambient
environmental noises such as ventilation fans or thunder can be ignored by
adjusting the microphones. The analyzer will count "events" such as
breaking glass, movement, and conversation, and declare an alarm when an
"overload" condition occurs (i.e., when the number of events succeeds a
preset number over a period of time). An alarm station operator can listen
to the cause of an alarm with an audio sensor's built-in assessment
capability. The following considerations for application and installation
apply to audio sensors:
a) These sensors are useful to both detect and assess duress
b) Ease of installation is often offset by cost-effectiveness
considerations when compared with other types of sensors and visual
c) Privacy shunts or cut-offs should be specified to preclude normal
d) Alarm station operator overload can easily occur in multiple
alarm assessment situations