A door alarm sensor detects a change in the relative position of a protected door or window and its sensing counterpart. In a typical magnetic contact, one part contains the sensing element and the other contains a magnet. When the opening moves across the device’s defined trigger point, the sensor changes state and a connected alarm system can apply the configured zone logic.
That state is usually interpreted as open or closed. It does not prove that the door is locked or unlocked. Lock status requires a separate source of evidence, such as a supported lock-state input or access-control event.
This guide explains the terminology, sensing methods, product types, selection inputs, placement decisions, commissioning checks and failure modes that installers and project teams should work through. Exact model and commercial evaluation belongs on the Door Magnetic Sensor product page; this article owns the method for making and validating the application decision.
What is a door alarm sensor?
A door alarm sensor is an opening detector used to identify when a door, window, hatch, shutter or another protected opening changes from its expected position. It can be a simple electrical contact, a battery-powered wireless device, a recessed detector or a multi-sensor device that also evaluates movement, shock, tilt or attempts to spoof the magnetic field.
In a hub-connected alarm system, the practical event path is:
Opening and sensing counterpart → sensor state change → enrolled zone at the hub → configured local alarm, app notification and/or monitoring event.
Each arrow is a separate verification point. A contact changing state does not prove that the hub received it. A hub event does not prove that the siren, app or alarm receiving centre received or interpreted it. Test only the paths included in the project and record the result at each layer.
For a wider view of field devices, hub logic and response paths, see the wireless security alarm system portfolio. For exact hub interfaces and current variants, use the Smart Hub route.
Door-contact terminology without the ambiguity
Different suppliers, installers and tenders may use overlapping names. Confirm what the term means in the exact document instead of treating every name as the same device.
| Term | Usually means | What it does not prove |
|---|---|---|
| Door alarm sensor | General term for an opening detector used in an alarm application | Sensing technology, protocol, lock state or monitoring path |
| Door/window contact | Contact-style detector used on an opening | Whether it is wired, wireless, surface mounted or recessed |
| Magnetic contact | A sensor and magnetic counterpart whose relative position changes the contact state | A universal gap, orientation or magnet polarity |
| Reed switch | A magnetically operated electrical switch used in some contact sensors | That every door sensor uses a reed switch or has the same contact logic |
| Hall-effect sensor | An electronic device that responds to a magnetic field and is used in some position-sensing designs | That it can replace any reed contact without circuit and mechanical redesign |
| Standalone door chime/alarm | A local device that may sound when an opening changes state | Hub supervision, app notification or professional monitoring |
| Hub-connected door sensor | A detector enrolled to a compatible hub and assigned to a zone | Universal compatibility with every hub, firmware, app or region |
“Normally open” and “normally closed” describe an electrical contact convention, not whether the physical door is open or closed. The system may also invert or rename a state in software. Document the physical door position, the electrical condition and the zone label separately during commissioning.
How magnetic door sensors work
Reed-switch designs
A reed switch contains ferromagnetic contacts sealed inside a small envelope. When a suitable magnetic field reaches the switch in the intended geometry, it can cause the contacts to change electrical state. When the field moves away, the contacts return according to the switch design. Littelfuse’s reed switch and reed sensor activation note shows that activation distance and behaviour depend on the magnet’s path and orientation relative to the switch.
This is a magnetic switching action—not a harmonic oscillator. It also means there is no sound universal rule such as “any magnet within 10 mm means closed.” The switch, magnet, enclosure, approach direction, mounting material and product thresholds all affect the result.
Hall-effect and other magnetic-sensing designs
Some designs use a Hall-effect device or another magnetic sensor instead of, or in addition to, a reed switch. Texas Instruments’ Hall-effect sensor explanation describes how a Hall element converts a magnetic field into a voltage that electronic circuitry can process. A product may use this information for position, direction or magnetic-field analysis, but only the exact product documentation defines what it reports.
Do not write “Hall sensor” into a specification unless the model’s current evidence says so. Likewise, do not assume a reed-switch device has anti-masking, direction sensing or field-strength analysis.
From contact state to alarm action
The sensing element provides an input; it does not decide the complete response by itself. The device and hub may apply enrollment, supervision, tamper, entry-delay, chime, arming-state and notification rules. A monitoring event exists only when a supported path has been configured and accepted by the receiving side.
The RBF Protocol overview explains the field communication layer used by selected Roombanker devices. It is not a universal compatibility statement: confirm the exact sensor model, regional variant, hub, firmware and project configuration.
Types of door alarm sensors and their trade-offs
| Type | Where it can fit | Main advantage | Main trade-off or evidence needed |
|---|---|---|---|
| Wired contact | New construction, existing alarm cabling, metal doors or long-life fixed infrastructure | Simple field contact and no sensor radio battery | Cable route, contact type, resistance/EOL requirements, panel input and tamper method must match |
| Wireless contact | Retrofit or sites where new cabling is impractical | Faster physical deployment and flexible placement | Exact hub/protocol/region, signal at final position, battery maintenance and supervision must be confirmed |
| Surface-mounted contact | Most visible door/window frames with suitable flat surfaces | Accessible for alignment, testing and service | Appearance, adhesive/screw method, clearance and impact exposure |
| Recessed contact | Openings where concealed installation is required and the construction permits it | Discreet finish | Drilling, void depth, cable access, fire-door/window restrictions and serviceability |
| Simple opening contact | Projects that only need an opening-state input | Clear event purpose and simpler commissioning | Does not provide shock, tilt, masking or lock-state evidence |
| Multi-sensor contact | Openings that require additional supported shock, tilt or anti-masking functions | More event types from one documented device | Orientation, thresholds, zone mapping and separate tests for every enabled function |
| Indoor model | Protected internal environments within the documented limits | Appropriate when exposure is controlled | Must not be moved outdoors by assumption |
| Environment-suitable model | Gates, shutters or exposed openings when explicitly rated and documented | Designed for the stated exposure class | Ingress rating, temperature, UV, condensation, mounting hardware and cable entries still need site review |
| Standalone chime/alarm | A local reminder or simple unmonitored use | Works without a full hub workflow when designed that way | May not provide supervision, remote events, system arming or ARC integration |
| Supervised hub-connected sensor | Alarm systems that need zone identity, supervision and configured response | Can participate in a documented system workflow | Support depends on exact device, hub, firmware, app and market variant |
When an existing third-party wired contact must be brought into a compatible wireless system, evaluate the wired-to-wireless alarm transmitter against its exact current specification. A transmitter is not a wiring accessory for Roombanker’s own wireless sensors, and no input type should be assumed without the model document.
Select a door alarm sensor from the opening and response plan
Begin with the opening, not the catalogue. Record the following inputs before selecting a model.
| Selection input | Questions to answer | Why it changes the decision |
|---|---|---|
| Opening type | Hinged, sliding, tilt-and-turn, roller shutter, hatch, gate or window? | Changes the travel path, alignment and suitable sensor form |
| Frame and moving surface | Timber, uPVC, aluminium, steel, glass or mixed construction? | Affects fixing method, magnetic behaviour, recess options and service access |
| Closed geometry | Are the surfaces flush, offset, angled or separated by a large gap? | Determines whether the sensor and counterpart can enter the documented trigger geometry |
| Movement and clearance | Which direction does the opening travel? Could either part collide, scrape or be struck? | Determines orientation, safe spacing and cable protection |
| Environment | Indoor, outdoor, cold store, dusty workshop, humid area or direct sun? | Determines required environmental evidence and mounting materials |
| Tamper exposure | Can the public or an intruder reach the sensor, magnet, cable or fixings? | May require tamper detection, concealed mounting or protected routing |
| Detection need | Opening only, or supported shock, tilt, masking or another condition? | Prevents buying a simple contact for an unsupported event |
| System fit | Which hub/panel, protocol, regional band and firmware are in scope? | Prevents model-family and cross-region substitutions |
| Power and maintenance | Wired input or battery? Who inspects and replaces the power source? | Creates a maintenance obligation and access requirement |
| Zone behaviour | Entry/exit, perimeter, chime, 24-hour, delayed or another approved zone type? | Changes how an otherwise identical contact event is handled |
| Response path | Local siren, RB Link, ARC integration or a defined combination? | Each path has different dependencies and acceptance tests |
A door sensor protects an opening; it is not a complete security design. A PIR motion sensor addresses movement in a coverage area, while an environmental monitoring sensor addresses a different hazard category. A Home Security Kit may provide a starting bundle, but the final device count and placement still come from the surveyed openings, movement routes, environment and response requirements.
For shops, offices, workshops and small warehouses, use the small-business security planning route to connect the opening decision to the wider site plan.
Place and mount the sensor for the actual movement
There is no universal rule that the sensor body must always be on the fixed frame and the magnet must always be on the moving leaf—or the reverse. Follow the exact model’s orientation and fixing instructions, then verify the installed movement.
- Observe the full travel. Open and close the door or window slowly. Identify rotation, sliding direction, flex, play, slam movement and any point where the parts could collide.
- Confirm the model-specific orientation. Use the manual’s marked side, alignment marks, magnet direction and permitted approach path. Do not infer magnet polarity from another product.
- Check both closed and trigger positions. The closed position must remain inside the accepted state under normal play; the opening must cross the trigger point early and repeatably enough for the project.
- Test more than one direction where relevant. Hinges, sliding tracks and tilt-and-turn windows can move the counterpart through different paths. The furthest-looking gap is not always the electrical transition point.
- Account for the frame material. Steel and other nearby magnetic material can change field behaviour. Thick profiles, reinforcement, seals and trim can also create offsets.
- Choose the fixing method deliberately. Adhesive can avoid drilling but depends on surface preparation, temperature, cure and long-term bond. Screws can improve mechanical retention but may be prohibited on fire doors, glazing systems or rented premises. Recessing can improve appearance but reduces access and requires construction approval.
- Keep the device serviceable. Batteries, tamper release, covers and serial labels must remain accessible without damaging the opening.
- Protect wired routes. Where a wired contact is used, protect the cable from hinge movement, sharp edges, crushing and unauthorised access.
The exact manual’s gap field is a model-specific test or specification—not a universal installation target. For example, the reviewed RBSS-MC1 documentation uses “Detection Gap >17 mm,” while the reviewed RBSS-MC2 specification lists “Detection Gap 17 mm.” Those fields must not be converted into “mount every sensor at 17 mm.” Install and test the exact model using its current instructions and the real opening geometry.
Roombanker example: RBSS-MC1 and RBSS-MC2 are not interchangeable claims
The following comparison uses the public Wiki pages reviewed on 15 July 2026. It is an evidence boundary, not a promise of current availability or universal compatibility.
| Evidence field | RBSS-MC1 Door Magnetic Sensor | RBSS-MC2 Door/Window Anti-masking Sensor | Project implication |
|---|---|---|---|
| Documented sensing | Reed switch | Two reed switches, accelerometer and magnetic sensor | Do not describe MC1 as having MC2 event functions |
| Documented functions | Opening contact; rear tamper; signal-strength test; low-battery notification | Opening, shock with three levels, tilt threshold field, anti-masking/magnet-spoofing logic, rear tamper, signal-strength test and low-battery notification | Enable and test only functions supported by the exact model and hub configuration |
| Documented variants | RBSS-MC1-868 and RBSS-MC1-915 | RBSS-MC2-868 and RBSS-MC2-915 | Match the regional variant to the selected system and market |
| Documented power | One AA battery | One CR123A battery | Maintenance plans and spares are model specific |
| Extra wired input | Not listed in the reviewed MC1 specification | Terminal for a third-party detector is listed in the reviewed MC2 specification | Input type, wiring, event mapping and compatibility still require the exact current instructions |
| Source | MC1 specification and MC1 quick-start guide | MC2 specification | Record source URL, model, revision/date and project conditions |
Do not infer market availability, finished-system certification, service life or compatibility from this table. Confirm the current document, firmware, hub, regional model and required evidence before a bill of materials or tender response.
Commission the door sensor as a complete zone
Physical mounting is only the beginning. Commission the exact device in its final location.
- Record the model, regional variant, serial number, battery or wired-input details, hub/panel and firmware.
- Enrol the device using the supported method and confirm it appears only once in the intended system.
- Give the zone a name that identifies the actual opening, such as “Ground Floor Rear Delivery Door,” rather than “Sensor 3.”
- With the opening fully closed, confirm the physical position, electrical/contact state and displayed zone state.
- Open the door slowly and record where the state changes. Repeat from normal operating speeds and relevant movement directions.
- Close and reopen the opening at least several times. Include normal frame play, latch pressure and expected vibration without damaging the opening.
- Test signal quality at the final mounted position using the supported method; do not rely on a bench test beside the hub.
- Test rear tamper, battery/low-battery, supervision or additional shock/tilt/masking functions only where the exact device and system support them.
- Apply the approved zone type, entry delay, chime and arming behaviour. Verify the result in armed and disarmed states as the project requires.
- Test the local siren or other on-site response included in scope.
- Test the app event, user permissions and notification settings if RB Link is in scope.
- Where monitoring is included, run a witnessed event with the ARC and confirm the account, zone label, event meaning and restoration.
- Hand over the opening name, device identity, placement record, configuration, test result, maintenance owner and unresolved exceptions.
The Roombanker Support centre is the route for current public manuals and help. A commissioning record should still identify the exact source used; “followed the website” is not enough for future maintenance.
Troubleshoot by symptom, check and action
| Symptom | Check first | Corrective action and retest |
|---|---|---|
| Zone stays open when the door is closed | Physical alignment, orientation, state naming, magnet path and exact manual | Reposition within the permitted geometry or correct the configured state; repeat slow and normal-speed tests |
| Zone stays closed when the door opens | Magnet remains within the sensing field, second magnet/metal nearby, incorrect input logic or wrong zone | Remove unintended magnetic influence, correct wiring/logic or revise placement; verify the real trigger point |
| Intermittent events | Frame play, loose fixing, adhesive movement, slamming, hinge wear or marginal trigger position | Stabilise the parts, use an approved fixing method and create sufficient model-specific operating margin |
| False opening during vibration | Loose door, flex, shock function/threshold, contact bounce or poorly selected zone logic | Repair the opening, review supported threshold/zone settings and test with representative vibration |
| Works on the bench but not installed | Final-position signal, metal/frame influence, hub distance, obstruction or battery state | Run the supported signal test in place, change one variable at a time and record the accepted arrangement |
| Device drops offline or reports supervision trouble | Battery seating/state, regional variant, enrollment, signal and supported supervision interval | Correct power or enrollment, redesign placement if needed and observe for the defined acceptance period |
| Adhesive pad releases | Surface contamination, incompatible finish, temperature, cure time or mechanical load | Prepare the surface and use a model-/surface-approved fixing method; do not remount onto failed adhesive |
| Tamper remains active | Cover seating, rear surface contact, fixing pressure or damaged tamper part | Reseat or refit according to the manual and verify tamper/restoration separately |
| App event missing but hub event exists | Hub internet, account role, app permissions, notification settings and supported model path | Isolate the app/cloud layer; do not remount a working sensor until the upstream path is tested |
| ARC receives the wrong or no event | Account, zone mapping, event code, receiver path and restoration logic | Correct the monitoring configuration and repeat a witnessed end-to-end test |
Change one variable at a time. Otherwise, a temporarily successful retest does not identify the failure boundary.
What evidence should remain after installation?
A maintainable door-contact record should include:
- Opening and zone name.
- Sensor model, regional variant and serial number.
- Hub/panel model and firmware or wired input identity.
- Source document URL and revision/date used.
- Sensor and counterpart positions, orientation and fixing method.
- Closed-state and trigger-point test results for relevant movement directions.
- Final-position signal result for a wireless device.
- Tamper, battery/supervision and any supported shock/tilt/masking tests.
- Entry-delay, chime, arming and local-response configuration.
- App and/or ARC witnessed result where included.
- Exceptions, maintenance owner and next review date.
This evidence lets a future installer distinguish a mounting problem from a device, radio, hub, app or monitoring-path problem.
Quick answers
Does a door alarm sensor tell you whether the door is locked?
No. A contact normally reports the relative position of the opening and its sensing counterpart. Closed-contact state is not proof that the lock or latch is engaged.
Is there a standard gap for every magnetic door sensor?
No. Trigger behaviour depends on the exact switch or sensing element, magnet, orientation, approach direction, enclosure, mounting material and product thresholds. Use the current model instructions and verify the installed opening.
Should the sensor body always go on the frame?
Not as a universal rule. Follow the exact model’s orientation and mounting instructions, account for the opening’s travel and frame material, and verify the closed and trigger states after fixing.
Can any wireless door contact work with any alarm hub?
No. Confirm the exact protocol, regional variant, hub, firmware, enrollment method, supported events and app/monitoring path.
What is the minimum useful commissioning test?
Identify and enrol the exact device, confirm closed and open states repeatedly at the final position, test signal and supported tamper/supervision, apply the approved zone behaviour, then test each required local, app and monitoring path separately.
When should a project use more than a simple opening contact?
Only when the risk assessment requires an additional event—such as supported shock, tilt or masking detection—and the exact device, placement, hub configuration and acceptance test can support it.
Make the next decision evidence-specific
For an exact Roombanker model review, use the Door Magnetic Sensor product page and request the current model, region, manual, compatibility and availability evidence. For a system design, bring the opening schedule, frame details, environment, response path and acceptance requirements rather than asking for a universal contact or gap.
The right door alarm sensor is the one whose sensing method, mechanical fit, system compatibility and response path can all be demonstrated at the actual opening.