microphone and an electronic processor which discriminates between "noise"
such as human speech and the specific frequency associated with a forcible
intrusion attempt. Both types of sensors are relatively low profile and
easy to install. They are difficult to defeat. Type selection depends upon
the propensity of the ambient environment to produce nuisance alarm stimuli.
18.104.22.168 Application and Installation Considerations. Several application
and installation considerations apply to vibration and ultrasonic
penetration detection sensors. For one, vibration sensors should not be
applied in situations where high vibrations are encountered such as on
shipboards, in proximity to heavy construction, on a railroad, or in heavy
vehicular road traffic. They cannot be used effectively outdoors, and they
do not function well on plastic or polycarbonate sheets. Both types of
sensors are relatively maintenance free when applied and installed properly
(including sensitivity adjustment) and are distributed by most quality
sensor manufacturers with an integrated battery backup. These sensors
should not be applied singly to cover an area (of glass) greater than 6 feet
square and should be applied in pairs to cover large areas (see Figure 17).
For multipane applications, two sensors should be specified to be applied to
the midpoints at the top and bottom of the area. Some portal
configurations, such as double hung or crank-out windows, dictate
application of the sensor(s) on the window of frames to provide effective
coverage. Lastly, testing and adjustment is usually accomplished with the
use of a "test device" consisting of a string-suspended ball which is
allowed to swing against the perimeter barriers (e.g., window pane) to
simulate a forcible intrusion attempt. This device, or a tuning fork for
ultrasonic sensor adjustment, is often offered as an extra cost option by a
"window bug" vendor. A low cost but effective alternative is to use a ring
of keys swung against the barrier (e.g., glass) as the adjustment stimulus.