On this page
- 01Before you start
- 02Where it sits in the project
- 03Main types of intrusion systems
- 04How the system works
- 05Main components
- 06Intrusion sensor technologies
- 07Zones, partitions and arming modes
- 08Layered detection strategy
- 09Specifications that matter
- 10Sizing rules and false-alarm reduction
- 11Communication, monitoring and integration
- 12Installation, testing and maintenance
- 13Choosing by application
- 14Check that it works
- 15Common problems and how to fix them
- 16Frequently asked questions
- 17Talk to PSS about intrusion alarm
An intrusion alarm system — also called an intruder or burglar alarm — detects unauthorized entry or suspicious activity in a protected area and generates alerts so a security response can follow. It is used in commercial buildings, offices, retail, warehouses, banks, industrial sites, data centres and homes. A modern system is more than a panel with a few motion detectors: magnetic contacts, glass-break detectors, motion sensors, shock and vibration devices, perimeter protection and specialised sensors report to a control panel that manages zones and partitions and drives local or remote notification.
The siren is the least valuable part. What matters is that each loop is provably intact, that only authorised people can arm and disarm, and that an alarm reaches a responder with a location attached. The system does not physically stop every break-in; it detects defined events and communicates them reliably.
Before you start
- Which EN 50131 grade the insurer or the client’s standard requires.
- Full schedule of openings with construction type (concrete, drywall, steel, shutter).
- Wired, wireless or hybrid — and whether perimeter wiring can still be installed.
- Who arms and disarms, at what times, and from where — and which partitions.
- Keyholders, response time, monitoring contract — who receives the alarm; dual path needed?
- Connectivity at the panel: network drop, GSM coverage.
- Power point, UPS and cabinet space; pets, curtains, air handling, false-alarm history.
- Integration: CCTV, access control, BMS, central security platform.
- Panic / hold-up, point protection or outdoor perimeter required.
- Testing, documentation and maintenance obligations.
Where it sits in the project
Small cable, big consequences. The system depends on the building’s openings (doors, windows, roof access, roller shutters), on a power point at the panel, on a network or cellular path for signalling, and on who responds. On most projects it arrives late — after ceilings close and doors are hung — which is exactly when perimeter contact wiring becomes impossible. Wired suits new construction and large commercial sites; wireless where cabling is disruptive; hybrid when an existing wired base must grow without extensive rewiring.
Main types of intrusion systems
| System type | Description | Typical applications |
|---|---|---|
| Wired | Sensors on dedicated cables or a wired bus | Commercial buildings, industrial sites, new construction |
| Wireless | Sensors on a supported radio protocol | Existing buildings, residential, difficult cabling |
| Hybrid | Wired and wireless devices on one compatible platform | Upgrades, mixed installs, expanding systems |
| Perimeter detection | Entry attempts at the envelope or external boundary | Windows, doors, fences, yards |
| Interior / volumetric | Movement inside rooms or spaces | Offices, corridors, warehouses, restricted areas |
| Point protection | Protects a specific asset, cabinet or safe | Banks, retail, server rooms, high-value storage |
| Commercial / enterprise | Scalable zones, partitions, central monitoring, integration | Multi-floor buildings, retail chains, campuses |
| High-security | Layered detection, tamper monitoring, supervised signalling | Critical facilities, sensitive installations |
Wired systems offer stable communication and less dependence on sensor batteries, but need planned cable routes and tamper protection. Wireless simplifies difficult routes; design must cover radio coverage, interference, battery life, device supervision and encryption where supported — wireless is not automatically less secure. Hybrid keeps wired devices while adding wireless areas; confirm panel, expanders, receivers, detectors and firmware compatibility.
How the system works
- Detection — a sensor sees an event (door opening, glass breaking, movement).
- Signal transmission — state or alarm signal reaches the panel.
- Event processing — the panel evaluates zone type, arming status, entry delay and programmed response.
- Alarm activation — if conditions are met, an alarm is generated.
- Local notification — sounder, siren, keypad or other configured output.
- Remote signalling — event sent to authorised users or a monitoring centre.
- Response and verification — responders assess and act.
- Event logging — history recorded where supported.
An entry-delay zone may allow time to disarm; an instant zone generates an immediate alarm while armed.
Main components
- Control panel — zones, partitions, user permissions, notification outputs, expansion, Ethernet/cellular communicators, battery supervision, tamper and health monitoring. Size it for zone count, sensor types, communication, expansion and security grade.
- Keypads and user interfaces — LCD, touchscreen, proximity credential, remote apps, authorised web or central security interfaces. Restrict administrative access; avoid shared or default credentials.
- Detectors — magnetic contact change, movement, glass-break acoustics, vibration or beam interruption.
- Sirens and sounders — indoor, outdoor weather-resistant, sounder/strobe; consider audibility, regulations and tamper monitoring.
- Communication modules — Ethernet/IP, cellular, dual-path communicator or other supported signalling. Dual path improves resilience only when the paths are configured and sufficiently independent.
- Backup power — battery sized from panel load, connected devices, standby period, alarm load and project requirements.
- Expansion modules and interfaces — additional inputs/outputs, remote keypads, readers, building security platforms — within the manufacturer’s architecture.
Intrusion sensor technologies
No single detector identifies every intrusion event. A reliable installation combines technologies so the strengths of one cover the limits of another.
Magnetic door and window contacts
A magnetic contact (reed switch) has a magnet on the moving leaf and a switch on the frame. When the opening moves beyond the manufacturer’s operating gap, the contact changes state. Typical use: main and service doors, ground-floor windows, storefronts, emergency exits, restricted rooms and cabinets. Strengths: simple and reliable for openings; low power on many models; surface or recessed; good perimeter layer. Limits: alignment and gap matter; large metal doors and rolling shutters need suitable contacts; a contact detects opening — not glass breaking or room movement.
Glass-break detectors
Used for large windows, storefront glazing and glass doors.
| Feature | Acoustic glass-break | Shock / vibration |
|---|---|---|
| Principle | Analyses sound patterns of breaking glass | Detects physical impact or vibration |
| Installation | Typically inside the protected space | Often on or near the protected surface |
| Advantage | Can cover suitable glazing without contacting every pane | Detects physical attack on the surface |
| Limitation | Depends on acoustics and rated coverage | Environmental vibration can affect sensitivity |
Some products combine acoustic and shock detection. Never assume one detector protects every window in a room — coverage, glazing type and room layout decide the count and placement.
PIR, dual-technology, microwave and curtain detectors
PIR (Passive Infrared) detects changes in infrared energy in its field of view. It does not transmit infrared for ordinary motion sensing. Typical for offices, retail, corridors, warehouses and residential interiors. Mounting height is usually 2.1–2.4 m. Avoid strong heat sources, direct sunlight and HVAC airflow; furniture and racks can block coverage. Pet-tolerant models exist (often quoted up to about 25 kg) with the correct lens.
Dual-technology commonly combines PIR and microwave, often requiring both technologies (AND logic) before alarming — useful where false-alarm resistance matters. Dual tech does not eliminate all false alarms; microwave coverage may extend beyond intended walls and must be verified.
| Feature | PIR | Dual-technology PIR + microwave |
|---|---|---|
| Technologies | Passive infrared | PIR and microwave |
| Advantage | Simple and effective for many indoor spaces | Can reduce certain unwanted alarms when correctly installed |
| Watch-outs | Heat, sunlight, airflow, obstructions | Same PIR factors plus microwave spill beyond boundaries |
| Typical use | Offices, rooms, corridors, residential | Commercial spaces needing extra false-alarm resistance |
Microwave-only detectors analyse changes in reflected electromagnetic energy; position carefully so the field does not spill into adjacent spaces. Curtain detectors create a narrow field along a window line, doorway or corridor — the term describes the coverage pattern, not one universal technology.
Outdoor, shock, seismic, beam and perimeter sensors
Outdoor motion detectors (PIR, microwave or combined) suit entrances, façades, service yards and loading areas. Account for wind, temperature, sunlight, animals and vegetation. Shock / vibration detectors sense physical disturbance of doors, windows, cabinets, safes or walls — useful before full opening; sensitivity must match the environment. Seismic detectors are specialised for attack vibration on safes, vaults and reinforced structures — not interchangeable with ordinary vibration sensors.
Photoelectric beams establish a detection line between transmitter and receiver (or reflector). Used for perimeters, openings, warehouses and outdoor approaches. Need alignment and a clear path; rain, dust, vegetation and movement can affect outdoor units. Fence-line beams often quote 50–200 m ranges; the real maintenance cost is re-alignment after wind and vegetation — plan the service visit into the contract.
Fence and perimeter systems may use fence-mounted vibration, specialised cables, outdoor beams, radar or other technologies — site-specific design. Roller shutter / specialised door sensors must match the mechanical movement of large openings. Panic / hold-up buttons are deliberately activated by a person; route the event to the right recipient and decide whether audible signalling is appropriate. Point-protection sensors cover cabinets, objects or small high-value areas.
Sensor comparison at a glance
| Sensor type | What it detects | Typical installation | Main limitation |
|---|---|---|---|
| Magnetic contact | Opening of a door or window | Leaf and frame | Does not detect all forced-entry methods |
| Acoustic glass-break | Sound of breaking glass | Inside the room | Acoustic conditions and coverage limits |
| Shock / vibration | Physical impact | Protected surface | Environmental vibration |
| PIR | Infrared changes from movement | Indoor room or corridor | Needs clear field of view |
| Dual-technology | Movement via two technologies | Selected commercial interiors | Still needs correct placement |
| Photoelectric beam | Beam interruption | Opening or perimeter line | Alignment and clear path |
| Seismic | Attack vibration on robust structures | Safe, vault, specialised asset | Application-specific selection |
| Panic button | Deliberate human activation | Reception, counter, workstation | Depends on correct use and response |
Zones, partitions and arming modes
A zone is a monitored input or logical detection area — often one door contact, one PIR or another supported input. Clear names (Main Entrance Door, Server Room, Loading Bay) help operators identify the source quickly. One zone per perimeter device — never mix a door contact and an interior PIR on the same zone: the operator loses the location and servicing becomes guesswork.
A partition is an independently controlled section of the system with its own arming state, user permissions and rules — for example Administration, Warehouse and Restricted Equipment Room.
| Feature | Zone | Partition |
|---|---|---|
| Definition | Monitored input or logical detection area | Independently controlled section of the system |
| Primary function | Identifies where an event occurs | Defines which group of zones arms/disarms together |
| Example | Rear Door Contact | Warehouse Partition |
Arming modes (names vary by panel):
- Away — premises unoccupied; typically enables perimeter and interior detection.
- Stay / Home — occupants remain; often arms contacts while bypassing designated interior motion.
- Night — selected perimeter and internal zones armed; designated living spaces remain free.
- Instant — removes entry delay on applicable zones; opening generates an immediate alarm.
- Partial — selected zones or areas only (Stay, Night, partition-based or manufacturer-specific).
- Automatic — schedule-based arming; configure carefully to avoid arming while occupied or with a zone not ready.
Exit delay gives time to leave after arming; entry delay gives time to disarm after entering a designated access point. Timing must match the real door: a 45-second entry delay on a door that takes 60 seconds to reach is a false alarm every morning. Not every zone should have an entry delay.
Layered detection strategy
- Perimeter — contacts, glass-break, shock on doors, windows and shutters; catch the opening or attack at the boundary.
- Interior — PIR / dual-tech in rooms and corridors; catch an intruder who bypasses the perimeter.
- Point — safe, cabinet, enclosure or sensitive storage.
- External perimeter — outdoor detectors, beams or fence systems where layout, environment and response make earlier warning useful.
Each sensor has limits. Combining complementary technologies improves coverage — without unnecessary complexity and unwanted alarms.
Specifications that matter
- Zone supervision. The EOL resistor belongs at the detector, not in the panel. Fitted at the panel, a cut cable reads as a healthy loop. Double-EOL lets the panel report alarm, tamper and fault as separate states — the baseline from Grade 2 upward.
- EN 50131 grades. Grade 1 low risk (opportunistic, basic residential); Grade 2 low-to-medium (typical residential, limited knowledge); Grade 3 medium-to-high (most commercial, reasonable knowledge); Grade 4 high (banks, museums, planned intrusion). Quote the grade in the offer — it drives detector quality, tamper protection and signalling.
- EN 50131-1 details: entry delay maximum 45 seconds at Grade 2; tamper detection mandatory from Grade 2; minimum user code length 5 / 6 / 7 digits at Grades 2 / 3 / 4; environmental classes I–IV per EN 50130-5.
- Signalling. EN 50136 defines transmission-path performance; SIA DC-09 over IP is common. Dual path means two different media, each independently supervised — not two SIMs from the same operator.
- Confirmed alarm. Two different detectors activating within a defined window (often 30 minutes) before the event is passed to a monitoring centre — the mechanism that cuts police-attended false alarms.
- Standby battery. A 12 V 7 Ah block in the panel is normal; standby time is whatever the actual load allows — calculate it.
| Grade | Risk level | Examples | Design impact |
|---|---|---|---|
| Grade 1 | Low | Basic residential | Basic detectors; tamper optional |
| Grade 2 | Low to medium | Residential, flats, shops | Tamper mandatory; max 45 s entry delay |
| Grade 3 | Medium to high | Most commercial projects | Higher-grade detectors; dual-path signalling |
| Grade 4 | High | Banks, museums, critical sites | Layered coverage; documented maintenance |
Sizing rules and false-alarm reduction
Current budget. Panel 100–200 mA + detectors at 10–20 mA each + siren 0.5–1 A + communicator about 100 mA. With 30 detectors the quiescent load is roughly 0.35 A, so 7 Ah gives about 20 hours of standby — but the siren in alarm dominates the draw, which is why the siren often carries its own battery.
Zone count. Openings + interior volumes + tamper inputs + technical/fire inputs, then add 20% spare.
False-alarm reduction. Select detectors for the environment; place motion sensors correctly; avoid heaters, moving vegetation and strong airflow; use outdoor-rated devices outdoors; set sensitivity per manufacturer guidance; keep coverage clear of racks and furniture; test glass-break under specified conditions; check door/window alignment; supervise wireless batteries; train users on arming; investigate repeated alarms — do not simply disable the zone. Dual technology and verification help in selected applications; they do not replace design and maintenance.
Communication, monitoring and integration
Local sounders and sirens alert occupants or deter activity. Remote notification uses IP, cellular or a supported dual path to users or an Alarm Receiving Centre (ARC). Verify protocol compatibility with the monitoring service before specifying the panel.
Alarm verification may use additional sensors, operator assessment, CCTV or video verification — without introducing delays that conflict with high-priority response. CCTV integration can display cameras linked to an alarm zone, highlight events, bookmark recordings and help assessment — only if camera coverage and sensor placement were coordinated. Access control integration correlates door state with credential activity; may support door-forced / door-held-open reporting and authorised arming procedures. BMS may monitor selected status or fault points; it does not replace the panel’s alarm handling, history or security interfaces.
Cybersecurity and resilience: change default credentials; strong unique users; restrict remote access; apply firmware updates; segment security from general networks where appropriate; monitor communication faults and tamper; protect backups; document behaviour during network or power failure. Wireless systems need supervision and low-battery reporting.
Installation, testing and maintenance
Follow approved drawings and manufacturer instructions for mounting, cable routing, orientation, tamper protection and configuration. Commissioning typically confirms: every zone identity; each sensor’s intended function; programmed alarm response; arming/disarming and entry/exit delays; local sounders; communication to the monitoring destination; battery and power-fault indications; tamper and supervision; CCTV/access integration where specified; user training and handover documents.
Maintenance: inspect sensors and wiring, check batteries, review histories, confirm communication paths, test sirens, investigate repeats. Document and re-test any change to zones, placement, communication or logic before returning the system to service.
Choosing by application
| Application | Typical design priorities |
|---|---|
| Residential | Contacts, interior motion, convenient arming, remote notification |
| Offices | Perimeter, motion, partitions, access control integration |
| Retail | Storefront contacts, glass-break, motion, selected asset protection |
| Warehouses | Suitable motion, loading-door contacts, zoned coverage |
| Banks / high-value | Layered detection, specialised assets, supervised devices, monitoring |
| Data centres | Restricted rooms, contacts, motion, event correlation, access control |
| Industrial / outdoor | Detectors for noise, dust, vibration; site-specific perimeter |
| Campuses | Central monitoring, network resilience, consistent zone naming |
Specify required detection functions and performance — not merely a fixed sensor count.
Check that it works
- Every zone identity matches the drawing; one perimeter device per zone.
- Away, Stay and Instant behave as programmed; entry and exit delays match the real door path.
- EOL at the detector: cutting the cable reports fault or tamper, not a healthy loop.
- Local sounders and remote signalling reach the configured destination; dual path supervised independently where specified.
- Battery and power-fault indications work; wireless devices report low battery where used.
- Repeated walk-tests pass without false alarms from heaters, sunlight or airflow.
Common problems and how to fix them
EOL resistors fitted at the panel
A cut loop reads as healthy. Move the EOL to the detector end and re-test open-circuit and short conditions.
Motion detectors alone with no perimeter layer
An intruder may bypass interior PIR after opening a door. Add contacts, glass-break or shock on the envelope.
PIR facing a window, heater or air-conditioning stream
False alarms follow. Re-aim or relocate; keep clear of heat and airflow.
Glass-break installed without confirming coverage and glazing type
Missed breaks or unwanted trips. Count detectors from rated coverage, glazing and room layout; test under specified conditions.
Grade 2 in the tender, domestic-grade detectors supplied
Replace with grade-compliant devices and document the offer grade against the install.
No tamper on the external siren; installer code left at factory default
Fit supervised tamper; change installer and master codes; restrict administrative access.
Single unsupervised signalling path
Nobody knows it failed until an alarm goes missing. Specify dual independent media with path supervision, or accept and document the residual risk.
Poor zone naming and unsuitable partitions
Incidents become hard to investigate. Rename zones clearly and align partitions with how the building is armed.
Disabling a zone after repeated false alarms
Fix the cause — placement, environment, sensitivity, alignment — then re-test. Do not leave a blind spot permanently.
Detector mounted before the ceiling is finished, then buried behind a duct
Reposition for a clear field of view; record battery age and service history; schedule replacements.
Frequently asked questions
Is wireless less secure than wired?
Not automatically. Wireless needs radio coverage design, supervision, encryption where supported and battery monitoring. Wired needs planned routes and tamper protection. Choose by the building and risk, not by a slogan.
Why one zone per door contact?
So the operator knows which opening caused the event. Mixing a door contact with an interior PIR on one zone hides the location and slows service.
What does EN 50131 Grade 3 change on a commercial site?
Higher-grade detectors, mandatory tamper practices, stronger user-code rules and typically dual-path signalling expectations — quote the grade in the offer so the supply matches it.
Where should the EOL resistor sit?
At the detector. At the panel, a cut cable still looks healthy. Double-EOL separates alarm, tamper and fault from Grade 2 upward.
Can CCTV replace walk-testing after an alarm?
CCTV helps verification when cameras and sensors were coordinated. It does not replace correct zone programming, EOL supervision or commissioning walk-tests.
Talk to PSS about intrusion alarm
PSS designs, installs and maintains intrusion alarm systems for homes, offices and high-risk sites. Contact the PSS team to book a first site survey.
