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Which of the following is NOT a type of motion detector?

Which of the following is NOT a type of motion detector?

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A.
Photoelectric sensor

B.
Passive infrared sensors

C.
Microwave Sensor.

D.
Ultrasonic Sensor.

Explanation:
A photoelectric sensor does not detect motion; it detects a break in a beam of light.
A photoelectric system, or photometric system, detects the change in a light beam. These systems work like
photoelectric smoke detectors, which emit a beam that hits the receiver. If this beam of light is interrupted, an
alarm sounds. The beams emitted by the photoelectric cell can be cross-sectional and can be invisible or visible
beams. Cross-sectional means that one area can have several different light beams extending across it, which
is usually carried out by using hidden mirrors to bounce the beam from one place to another until it hits the light
receiver.
Incorrect Answers:
B: A passive infrared system (PIR) identifies the changes of heat waves in an area it is configured to monitor. If
the particles’ temperature within the air rises, it could be an indication of the presence of an intruder, so an
alarm is sounded. A PIR is a type of motion detector. Therefore, this answer is incorrect.
C: Wave-pattern motion detectors differ in the frequency of the waves they monitor. The different frequencies
are microwave, ultrasonic, and low frequency. All of these devices generate a wave pattern that is sent over a
sensitive area and reflected back to a receiver. If the pattern is returned undisturbed, the device does nothing. If
the pattern returns altered because something in the room is moving, an alarm sounds. A Microwave Sensor is
a type of motion detector. Therefore, this answer is incorrect.
D: An Ultrasonic Sensor is an example of a wave-pattern motion detector. Therefore, this answer is incorrect.

Harris, Shon, All In One CISSP Exam Guide, 6th Edition, McGraw-Hill, 2013, p. 495


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