1. Which of the following common construction materials can ultrasonic units penetrate?
   a. Glass
   b. Metal
   c. Sheet rock
   d. Wood
   e. All of the above
   f. None of the above
   
   
2. Which of the following common construction materials can PIRs penetrate?
   a. Glass
   b. Metal
   c. Sheet rock
   d. Wood
   e. All of the above
   f. None of the above
   
   
3. Which of the following can be used for outdoor motion detection?
   a. Microwaves
   b. Photoelectric beams
   c. Seismic detectors
   d. All of the above
   e. None of the above
   
   
4. Ultrasonic detectors typically operate in what frequency range?
   a. 20 KHz to 40 KHz
   b. 20 MHz to 40 MHz
   c. 20 GHz to 40 GHz
   d. All of the above
   e. None of the above
   
   
5. Dual beams are used in photoelectric detectors to increase catch performance.
   a. True
   b. False
   
   
6. PIR detectors typically operate in what frequency range?
   a. 20 KHz to 40 KHz
   b. 20 MHz to 40 MHz
   c. 20 GHz to 40 GHz
   d. All of the above
   e. None of the above
   
   
7. Increasing the range level in microwave detectors will increase catch performance close to the unit.
   a. True
   b. False
   
   
8. Which of the following is not considered a volumetric detector?
   a. Ultrasonic
   b. Microwave
   c. PIR
   d. Photoelectric beam
   e. None of the above
   
   
9. Dual-beam photoelectric beams should not be used for indoor protection.
   a. True
   b. False
   
   
10. The mounting height of a motion detector has no effect on its area of coverage.
    a. True
    b. False
    
    
11. Which of the following techniques do not utilize the Doppler shift principle to detect motion?
    a. Ultrasonic
    b. Microwave
    c. PIR
    d. All of the above
    e. None of the above
    
    
12. The wire entry openings should be sealed when installing motion detectors.
    a. True
    b. False
    
    
13. PIR detectors are most sensitive to motion toward and away from the unit.
    a. True
    b. False
    
    
14. According to UL, motion detectors can be used to provide complete protection for a vault door.
    a. True
    b. False

What’s Wrong with This?

Wally `Larman installed a burglar alarm system for a local electronics store using microwave detectors. He installed the devices as shown in this diagram, connecting each device to its own zone, and fully tested the system. Everything seemed to work properly, but the system frequently had false alarms from the truck bay microwave unit, especially during stormy nights. Wally replaced the unit and carefully adjusted its range, but the false alarms continued. Can you see what is causing the false alarms and what Wally can do to correct the problem? 

5-Minute Tech Quiz Answers

1.         f — Ultrasonic devices cannot penetrate any of these materials. However, microwave detectors can penetrate all of these common materials, except for metal, extending the detection area into unintended areas.

2.         f — Because PIRs do not transmit any energy, they cannot penetrate any type of construction material.

3.         d — All of these technologies can be used for outdoor protection. Care must be exercised when selecting outdoor detectors to ensure that the unit chosen is specifically designed for outdoor use.

4.         a

5.         b — Dual beams are employed to reduce false alarms caused by small animals, snow and blowing debris.

6.         e – Because PIRs are passive, they do not emit any energy.

7.         b — Increasing the range of a microwave detector will extend its area of coverage but not increase its catch performance.

8.         d

9.         b — Frequently dual-beam photoelectric units are installed indoors to overcome potential false alarms caused by birds or rodents.

10.       b

11.       c

12.       a — Sealing all openings of a motion detector will reduce false alarms caused by insects or severe drafts entering the unit.

13.       b — PIRs are most sensitive to motion across the area of coverage, while ultrasonic and microwave detectors are most sensitive to motion toward or away from the device.

14. b

Answer to: What's Wrong with This?

Wally’s problem is caused by the location of the microwave detector in the truck bay. Wally installed it so that it is looking directly at the overhead door, and during a storm or windy condition, the overhead door can move, causing the microwave to trip. This is particularly true if the door is constructed of steel, because steel is a good reflector of microwave energy. Wally should relocate the microwave detector in the truck bay so that it does not face the overhead door as shown in this diagram, carefully adjust its range and retest the system. You must be very careful when installing microwave detectors, because they can penetrate many common construction materials, allowing it to detect motion outside the protected area, which can result in false alarms.