🚧 Under construction — VoTechWorks is being built. A free tech program — complimentary, as our commitment to get America working.
voTechWorksGrade 13 · a vocational technology learning center, by urbanicity
newSchoolWorks.com › VoTechWorks › Business & Cross-Cutting › Locksmith & Security Systems › CCTV & Alarm System Installation › Lesson 3
BUS-LOCK72-06 · Lesson 3 · 16 clock hours · lab

Intrusion-Alarm Sensors, Zones, and Panel Wiring

Objective. Students will wire a minimum of six alarm zones including passive infrared motion detectors, door/window contacts, and a glass-break sensor to a control panel, apply end-of-line resistor supervision, and verify each zone trips and restores correctly.

⚠ Pending professional review

This lesson, its worked examples and its practice questions has not yet been verified by a credentialed professional in the field or by a certification or approval body. It is a study draft and may contain errors. Do not use it as instructions for work on a job site or on live equipment. Always follow your instructor, your supervising professional, and current official references and regulations.

VoTechWorks program approval and accreditation are still in progress. Credentials are issued only by the certifying bodies named in each program, after their own exams.

Intrusion-Alarm Sensors, Zones, and Panel Wiring

A hardwired intrusion-alarm system is only as reliable as its wiring. Every sensor—whether a passive infrared (PIR) motion detector, a magnetic door or window contact, or a glass-break sensor—must be wired correctly to the control panel, supervised against tampering or wire failure, and verified to trip and restore cleanly. This lab teaches you to do exactly that.

How Zones Work

A zone is one monitored circuit. The control panel continuously measures the electrical state of each zone loop. When that state changes outside its expected range, the panel flags an alarm or trouble condition.

Zone loops run in two basic configurations:

Neither raw NC nor raw NO wiring is supervised; a cut wire in an NC loop looks identical to an alarm condition and cannot be distinguished from a true fault without additional circuitry.

End-of-Line Resistor Supervision

Supervision solves the problem of distinguishing normal, alarm, and trouble states. A end-of-line (EOL) resistor is placed in parallel (or series, depending on the panel and configuration) with the sensor contacts—physically at the far end of the zone, away from the panel. The panel measures a specific resistance value under normal conditions, a different value under alarm, and an out-of-range or open/short reading under a wiring fault or tamper attempt.

A typical single-resistor supervised NC zone produces three measurable states:

| Panel reading | State |

|---|---|

| Resistor value (e.g., 1 kΩ or 2.2 kΩ) | Normal / Secure |

| Near 0 Ω (short) | Alarm (contact closed across resistor) |

| Open / infinite | Trouble (wire cut, tamper, or lost connection) |

Always use the resistor value specified in your panel manufacturer's documentation. Common values are 1 kΩ, 2.2 kΩ, 4.7 kΩ, and 5.6 kΩ; mixing values across panels or zones causes chronic false trouble conditions.

The EOL resistor must be placed at the sensor, not at the panel. Placing it at the panel defeats supervision: a wire cut between the panel and the sensor would not be detected.

Sensor Types in This Lab

PIR Motion Detectors sense infrared energy changes caused by a moving person. They have three connections: power (typically 12 VDC), ground (common), and a normally closed alarm output. Always observe polarity on powered detectors—reversed power will damage the device. Most PIRs also include a tamper switch that opens if the cover is removed; wire the tamper in series with the zone or to a dedicated tamper zone depending on panel capability.

Magnetic Door/Window Contacts are two-part devices: a magnet mounts on the moving sash; a reed switch mounts on the frame. When the door or window opens, the magnet moves away and the reed switch opens (in NC configuration), signaling alarm. Maintain alignment within the manufacturer's gap specification.

Glass-Break Sensors use acoustic detection to recognize the frequency pattern of breaking glass. They require 12 VDC power, ground, and an NC alarm output, and must be mounted within the detection range specified on the data sheet—placement too far away or around corners reduces reliability. Test with a dedicated glass-break simulator, not by breaking actual glass.

Wiring Procedure

1. Plan before you wire. Complete the zone-wiring diagram on your worksheet—sensor type, NC or NO, EOL resistor location and value—before handling any wire.

2. De-energize the panel. Disconnect AC power and the backup battery before opening the enclosure or connecting wires. This is a lockout/tagout discipline: confirm zero energy with your multimeter before working inside.

3. Run 18/2 wire from each sensor location back to the panel terminal strip. Leave service loops at both ends. Label both ends with zone number.

4. Install EOL resistors at the sensor end, soldering or using a proper in-line resistor housing. Protect joints with heat shrink or electrical tape.

5. Connect powered sensors (PIR, glass-break) to the auxiliary power terminals. Verify voltage polarity before energizing.

6. Connect zone pairs to the correct zone terminals on the panel strip—observe polarity where required.

7. Reconnect battery first, then AC power. This order protects the panel if the AC connection is momentarily shorted.

8. Verify each zone with a multimeter before initiating panel programming. Confirm the zone reads within the supervised resistance window. Then walk the zone—open the contact or actuate the sensor—and confirm the panel LED and keypad display indicate alarm, then restore.

Safety Points

Fault Diagnosis

Use your multimeter in resistance (Ω) mode at the panel terminal with the panel de-energized. Compare your reading against the panel's supervision table. Readings near 0 Ω indicate a short; infinite or open readings indicate a broken conductor, disconnected termination, or a tamper loop that is not closed. A reading that is the correct resistor value but doubled may mean two resistors are in the circuit instead of one. Document each fault in writing before correcting it—this mirrors real service-call documentation practice.

Key terms9

ZoneA single monitored circuit loop on a control panel; the panel tracks the electrical state of each zone to detect alarm or fault conditions.
End-of-Line (EOL) ResistorA resistor placed at the far end of a zone loop that allows the panel to distinguish three states—normal, alarm, and trouble—by measuring loop resistance.
Normally Closed (NC)A circuit configuration in which current flows continuously under normal conditions; breaking the circuit signals an alarm.
Passive Infrared (PIR) DetectorA powered motion sensor that detects changes in infrared energy caused by a moving person; requires a DC power connection in addition to its alarm output wiring.
SupervisionThe use of EOL resistors (or other techniques) to allow a control panel to continuously monitor zone wiring for open-circuit or short-circuit faults, not just alarm conditions.
Tamper SwitchA mechanical switch built into a sensor enclosure that opens when the cover is removed, signaling an attempt to defeat the device.
Magnetic ContactA two-part intrusion sensor consisting of a reed switch on a fixed frame and a magnet on the moving door or window; separation of the two parts changes the circuit state.
Glass-Break SensorAn acoustic detector that recognizes the specific frequency pattern produced when glass breaks; must be mounted within manufacturer-specified range and tested with a simulator.
Backup BatteryA sealed lead-acid or similar secondary power source connected to the alarm panel that maintains system operation during an AC power failure.

Worked examples4

1. A panel uses 1 kΩ EOL resistors. With the zone at rest (secure), what resistance should a technician read across the zone terminals, and what reading would indicate an open-circuit fault?
  1. In a supervised NC zone, the EOL resistor is wired in parallel with the normally closed sensor contacts.
  2. When the zone is secure, the contacts are closed (0 Ω path), placing the 1 kΩ resistor in parallel with a short circuit.
  3. A resistor in parallel with 0 Ω equals 0 Ω — but that is the unsupervised case. In a properly supervised single-EOL wiring scheme, the resistor is placed in the loop so that the closed contact puts the resistor in parallel across the panel terminals. The panel sees 1 kΩ at rest.
  4. If the wiring opens (wire cut or connector loose), the closed-contact path is broken and the resistor is no longer completing the circuit; the panel reads infinite (open) resistance.
  5. Therefore: normal reading = 1 kΩ; open-circuit fault reading = infinite / OL on a multimeter.
Answer: Normal (secure) zone: approximately 1 kΩ. Open-circuit (wire cut or lost connection) fault: infinite resistance (OL on multimeter display).
2. A technician measures a zone resistance of approximately 0 Ω (near zero). The sensor contacts are in the closed/secure position. What fault does this indicate, and why?
  1. Under normal supervised operation with the sensor contacts closed, the expected reading is the EOL resistor value (e.g., 1 kΩ), not zero.
  2. A reading near 0 Ω means the zone terminals are shorted — current has a direct path with essentially no resistance.
  3. This could be caused by a short circuit in the wiring (two conductors touching), a failed sensor presenting a bolted short, or—in some wiring configurations—the resistor being inadvertently bridged by a staple or damaged insulation.
  4. The panel interprets a near-zero reading as an alarm condition (contacts opened, shorting the resistor out) or a short-circuit trouble, depending on panel logic. Either way it is a wiring fault.
Answer: A near-zero resistance reading indicates a short-circuit fault: the zone conductors are touching or a component is shorted. The reading is not the expected EOL resistor value, so there is a wiring problem that must be located and corrected.
3. A panel supervision table says the normal zone window is 900 Ω to 1,100 Ω (for a 1 kΩ EOL resistor). A technician measures 2,050 Ω on zone 4. What is the most likely cause?
  1. The expected reading is approximately 1 kΩ (within the 900–1,100 Ω window).
  2. 2,050 Ω is approximately twice the expected value.
  3. If two 1 kΩ EOL resistors are placed in series in the same zone loop, the total resistance would be 1,000 + 1,000 = 2,000 Ω, which is close to the measured value.
  4. This most likely means a second EOL resistor was inadvertently installed—possibly at the panel as well as at the sensor—creating a series resistance that doubles the zone reading.
  5. Corrective action: locate and remove the extra resistor, retaining only the one at the sensor end.
Answer: Approximately 2,050 Ω is consistent with two 1 kΩ resistors wired in series in the zone loop. The extra resistor should be located (likely at the panel end) and removed, leaving only the EOL resistor at the sensor.
4. A PIR detector is powered by the panel's 12 VDC auxiliary output. The technician connects the red wire to the negative terminal and the black wire to the positive terminal. What is the likely result, and what should the technician do before powering up?
  1. Most PIR detectors require correct DC polarity. Reversing polarity—positive to the negative terminal and vice versa—can damage or destroy the detector's internal electronics.
  2. Before powering up, the technician should de-energize the panel (disconnect AC and battery) and verify wire color conventions against the manufacturer's wiring diagram, not assumed color codes.
  3. Industry convention is red = positive (+) and black = negative (−), but the technician must always confirm with the manufacturer data sheet because some manufacturers use different colors.
  4. Correct the connections so red goes to positive and black to negative (or per the data sheet), then re-energize and verify the detector powers up and the alarm LED behaves correctly.
Answer: Reversed polarity will likely damage the PIR detector. The technician must de-energize the panel, verify polarity markings on the detector and panel against the manufacturer wiring diagram, correct the connections (red to +, black to −, or as specified), then re-energize.
In class: Zone-wiring diagram exercise: students read a written zone plan specifying sensor type, normally-open or normally-closed circuit configuration, and supervision requirement, then draw the complete wiring schematic for each zone including end-of-line resistor placement before touching any wire. · Physical panel wiring lab: using the approved schematic, students mount sensors on a door/window mock-up and wall, run 18/2 back to the panel terminal strip, install end-of-line resistors, and connect the panel power supply and backup battery following the manufacturer wiring diagram. · Zone-fault diagnosis drill: instructor secretly introduces four wiring faults (open circuit, short, missing resistor, reversed tamper loop); students use a multimeter to measure zone resistance, compare readings against the supervision table, identify each fault in writing, and correct it.
Materials: Alarm control panel (minimum 8-zone), PIR motion detectors, door/window magnetic contacts, glass-break sensor, 18/2 alarm wire, end-of-line resistors, backup battery, 12 VDC power supply, panel enclosure, multimeter, wire stripper, screwdrivers, mounting hardware, zone-plan worksheets, manufacturer programming manual
Check: Each of the six or more zones must read within the supervised resistance window (instructor verifies with multimeter) and must trip and restore cleanly on panel LED and keypad display; all four injected faults must be correctly identified and corrected — passing standard requires zero unresolved faults.

Practice check8

Answer each question, then check it. Nothing is recorded; this is your own practice.

Alarm system installation and supervision
1. Why must an end-of-line resistor be placed at the sensor rather than at the control panel?
Alarm system troubleshooting
2. A technician is testing zone 3 with a multimeter set to resistance. The panel uses 2.2 kΩ EOL resistors. The reading is 'OL' (overload/infinite). Which condition does this most likely indicate?
Safety and electrical hazard control
3. Which action should a technician take FIRST when opening an alarm control panel enclosure to rewire a zone?
Alarm sensor operation
4. A door contact sensor is installed on a hinged door in a normally closed configuration. When the door is closed (secure), how are the reed switch contacts positioned?
Alarm sensor installation
5. A glass-break sensor fails to respond during functional testing with a glass-break simulator. Which of the following is the MOST likely installation error?
Alarm system installation procedures
6. When reconnecting power to a control panel after completing a wiring repair, which sequence is correct?
Alarm system troubleshooting
7. During a zone-fault diagnosis drill, a technician measures approximately 500 Ω on a zone configured for 1 kΩ EOL supervision. The sensor contacts appear closed (secure). What is the most likely cause?
Alarm system components and security
8. Which of the following best describes the purpose of a tamper switch on an alarm sensor enclosure?
Record this lesson on my transcript. Sign in with your key and enrollment email to record lessons (enroll free if you have no key). This page stays open to read and practise.
← Previous lessonProgram planNext lesson →