alarm wiring diagram

Alarm Wiring Diagram — circuit diagram showing component connections+-12V SupplyControl SwitchKRelay CoilFlyback DiodeRelay Contact (NO)Lamp (Load)Relay Control CircuitFlyback diode protects coilNO contact closes when coil energized
alarm wiring diagram — interactive diagram. Open it in the editor to customise components and wiring.

This is a free printable alarm wiring diagram: download the diagram as SVG or open it and print to paper or PDF.

An alarm wiring diagram illustrates the electrical connections for home or commercial security alarm systems including door/window sensors, motion detectors, control panel, siren, and monitoring station communication. The diagram shows: door/window sensors connected in series on zone circuits (typically 4 zones: entry, interior, perimeter, auxiliary), each sensor containing a magnetic reed switch that opens when the door/window separates, signaling a violation to the control panel. Motion detectors (passive infrared) monitor interior rooms and transmit detection to the control panel via hardwired or wireless signals. The control panel processes sensor inputs, compares against system state (armed/disarmed), and triggers appropriate responses: audible siren activation (85-120 dB), silent alarm alerting monitoring station, or both. The diagram shows: battery backup power (12V) maintaining operation during AC power loss, backup siren in case primary siren fails, and communication module transmitting alarm signals to the monitoring station via phone line or internet. Modern alarm diagrams include: wireless zone sensors eliminating hardwiring, smartphone app integration enabling remote monitoring, and integration with smart home systems controlling lights and locks during alarm events.

How to wire alarm wiring diagram

  1. Plan zone layout and cable routes before installation Draw a floor plan, mark all detector positions, and plan cable routes through ceiling voids back to the panel location. Poor cable planning results in visible surface-mounted conduit and difficult future fault finding.
  2. Install panel in a secure, central location Mount the panel in a lockable enclosure in a concealed location — linen cupboard or ceiling void. Position near a 220V supply for the transformer. Keep panel accessible for programming and servicing.
  3. Run detection cable to each zone Run 6-core shielded cable from each detector position back to the panel. Use ceiling voids where possible. Label each cable at both ends immediately — never rely on memory to identify cables later.
  4. Wire detectors in NC series loops per zone Wire each detector's NC contacts in series along the zone cable. Install the EOL resistor at the last detector in each zone. Return the loop to the panel zone terminal and COM terminal.
  5. Wire siren, strobe, and keypad Connect siren trigger output from panel to siren module. Run 4-core data bus cable to keypad. Connect siren tamper loop back to panel tamper zone. Fit siren with security screws only.
  6. Connect power supply and backup battery Wire 220V transformer to panel input. Connect sealed lead-acid battery to battery terminals — positive then negative. Panel should power up and display low-battery fault until battery charges above threshold.
  7. Program zones, entry/exit delays, and test all detectors Program zone types, entry delay, exit delay, and alarm output timers per the panel manual. Walk-test each PIR and open each door contact to confirm panel registers the zone fault. Do not hand over without full system test.

Frequently asked questions

Why does my alarm trigger randomly during load shedding?

The control panel's backup battery is likely failing. When Eskom power drops, a weak battery cannot maintain the panel's regulated 12V supply, causing the microprocessor to reset and trigger a fault alarm. Test battery voltage under load — it should hold above 11.5V. Replace if it drops below 10.5V under panel load.

What is the difference between an NC and NO zone wiring configuration?

NC (normally closed) zones wire detectors in a series loop — a break anywhere in the loop triggers the alarm. NO (normally open) zones trigger on contact closure. Almost all professional alarm installations use NC zones with end-of-line resistors because a cut wire is detectable as a tamper, not silence.

What is an end-of-line resistor and why is it important?

An end-of-line (EOL) resistor installs at the last detector in each zone. The panel monitors the loop resistance continuously. A short circuit reads as zero ohms (tamper), a break reads as infinite ohms (open), and a normal closed loop reads the EOL resistor value. Without EOL resistors, a cut wire is undetectable.

My outdoor siren activates by itself at night. What is causing it?

Most likely the siren's internal tamper switch is triggering. Temperature cycling causes the siren housing to flex, momentarily operating the tamper contact. Alternatively, the siren's backup battery is failing, causing it to self-activate on low battery detection. Open and inspect — check tamper switch seating and battery voltage.

How many zones do I need for a typical South African home?

A standard 3-bedroom house typically needs: 1 zone per external door (2–3 zones), 1 zone per PIR covering open areas (2–3 zones), and 1 zone for the perimeter beam if fitted. A minimum 8-zone panel covers most homes comfortably, leaving spare zones for future expansion.

Related diagrams

Free electrical calculators

Edit this diagram free in the online editor