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Security systems practice questions

27 questions from the low voltage and structured cabling practice test.

Security systems practice test

10 questions, graded as you go, with the reason for every answer. No sign-up.

What this covers

Sample questions

Why is a dual-technology (PIR plus microwave) motion detector less prone to false alarms than a PIR alone?

  1. Either technology can trip the alarm independently
  2. Both technologies must detect at the same time to trip
  3. The microwave section doubles the coverage range
  4. The PIR section is switched off while the heater runs
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B. Both technologies must detect at the same time to trip

The two sensors react to different things, so requiring both to agree rejects causes that fool only one of them, such as a heating vent (PIR) or movement behind a thin wall (microwave). If either one alone could trip the alarm, false alarms would increase.

Reference: Intrusion detection principles; sensor manufacturer data

Several normally closed door contacts are to share one alarm zone. How are they wired?

  1. In parallel, so opening any one contact shorts the loop
  2. In series, so opening any one contact breaks the loop
  3. In parallel, so all contacts must open to break the loop
  4. In series, so all contacts must open to break the loop
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B. In series, so opening any one contact breaks the loop

Normally closed devices go in series: current flows through every closed contact and any one opening interrupts it. Normally open devices are the ones wired in parallel, so that any one closing completes the circuit.

Reference: Alarm circuit wiring fundamentals

Where should the end-of-line resistor be installed on a supervised alarm zone?

  1. Across the zone terminals inside the control panel
  2. At the first device on the loop, nearest to the panel
  3. At the midpoint of the cable run, inside a junction box
  4. At the last device on the loop, farthest from the panel
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D. At the last device on the loop, farthest from the panel

The resistor lets the panel see a known resistance through the entire length of the loop, so a short or open anywhere along the wire is detected. Fitting it at the panel terminals makes the panel happy but leaves the field wiring unsupervised.

Reference: Alarm zone supervision; control panel installation manuals

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