What is a magnetic alarm contact?
A magnetic door or window contact is a perimeter security sensor designed to detect the opening or closing of a protected access point. A typical contact uses two parts: a magnet mounted on the moving section and a reed switch or electronic sensing element mounted on the frame.
Doors
Protect exterior doors, pedestrian entrances, security doors, store rooms and other important access points.
Windows
Suitable opening windows can be protected where the contact can be securely installed and correctly aligned.
Commercial openings
Contacts can help monitor selected doors, cabinets, service entrances and other controlled openings in business environments.
Perimeter protection
Magnetic contacts complement motion detection by providing a direct opening-point detection layer.
How magnetic door and window sensors work
In a conventional magnetic contact, the magnet and reed switch are positioned close together when the door or window is closed. Opening the protected point separates the two components and changes the electrical state of the contact.
| Condition | Typical sensor state | Alarm system interpretation |
|---|---|---|
| Opening closed | Magnet aligned with contact | Zone generally remains normal |
| Opening moved | Magnet separates from contact | Zone can change state and trigger an alarm when armed |
| Contact damaged or wiring fault | Depends on circuit design | May create a trouble condition or alarm |
Exact zone behaviour depends on the alarm panel, contact type, end-of-line configuration and programming. A qualified installer should configure and test the complete circuit.
Wired vs wireless magnetic contacts
| Feature | Wired contact | Wireless contact |
|---|---|---|
| Connection | Cable to the alarm system or zone expander | Radio communication with a compatible receiver/panel |
| Installation | May require cable routing and access to the alarm wiring | Often easier where new cabling is difficult |
| Power | Usually supplied through the alarm circuit/design | Normally uses a replaceable battery |
| Maintenance | Inspect cable, terminals and physical mounting | Includes battery condition and wireless communication |
| Best fit | New builds, renovations or accessible cable routes | Existing buildings where minimising new cabling is important |
Where should magnetic contacts be installed?
Sensor placement should be based on the actual threat model and the way the opening operates. Exterior doors are usually high-priority perimeter points, while selected windows may be protected according to accessibility and risk.
- Prioritise accessible exterior doors and vulnerable openings.
- Mount the two sensor components securely so normal movement does not cause unreliable operation.
- Follow the contact manufacturer's permitted alignment and separation distance.
- Protect wiring from mechanical damage, tampering and accidental disconnection.
- Consider sliding doors and windows separately because their movement can require different mounting arrangements.
- Test every protected opening with the alarm panel after installation.
Magnetic contacts for different properties
Homes
Useful for front and back doors, garage access, selected windows and other perimeter points where opening detection is valuable.
Businesses
Can protect staff entrances, offices, storerooms, service doors and selected high-risk openings as part of a zoned alarm system.
Farms & outbuildings
Can be incorporated into suitable building alarms for offices, workshops, equipment rooms and other protected structures.
Magnetic contacts vs PIR motion sensors
| Characteristic | Magnetic contact | PIR motion sensor |
|---|---|---|
| Primary detection | Opening/movement of a protected point | Movement associated with changes in infrared energy |
| Typical location | Door or window | Room, passage, entrance or suitable outdoor area |
| Best strength | Direct perimeter opening detection | Interior movement detection |
| Common design use | Perimeter layer | Interior detection layer |
For many properties, the strongest alarm design uses complementary sensors rather than relying on a single sensor type. See our PIR Motion Sensors Guide and Alarm Systems Guide.
Common magnetic contact problems
False alarms
Check alignment, mounting, excessive movement, damaged wiring and zone configuration. Wireless contacts should also be checked for battery and communication issues.
Door shows open
The magnet may be too far from the sensor, misaligned, loose or incorrectly positioned. The zone and wiring should also be tested.
Intermittent faults
Movement, loose terminals, damaged cable, poor mounting or marginal wireless communication can produce intermittent conditions.
Wireless battery warning
Replace the battery with the correct type and follow the alarm manufacturer's procedure for maintaining and testing the sensor.
Security design considerations
Magnetic contacts are one component of a layered security system. For higher-risk properties, they can be combined with motion detection, CCTV, electric fencing, access control, panic devices, sirens and appropriate monitoring.
Explore related Nexpak guides: Wireless vs Wired Alarm Systems, Home Alarm Systems, Business Alarm Systems, and Alarm Installation Cost in South Africa.
Installation checklist
- Identify priority doors and windows based on the property's risk profile.
- Confirm the alarm panel supports the selected contact technology.
- Choose wired or wireless based on the building and installation route.
- Use compatible contacts and manufacturer-approved installation methods.
- Secure both contact components and verify their permitted operating gap.
- Check cable protection or wireless signal quality.
- Configure the correct alarm zone and end-of-line arrangement where applicable.
- Test opening, closing, arming and alarm conditions before handover.
- Document the protected zones so future maintenance is easier.
Frequently asked questions
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