How automatic doors for disabled access are planned in South Africa: swing or sliding, push plates and sensors, low-energy operation, load shedding and SANS 10400 Part S.
Automatic Door Sensors: Motion vs Presence
Almost every automatic door has two kinds of automatic door sensors doing two completely different jobs, and confusing them is the single most common reason a door misbehaves — or hurts somebody.
One opens the door. The other stops it closing on you. If you understand nothing else about automatic door sensors, understand that.
Motion automatic door sensors open the door
The motion sensor — the activation sensor — is the one people think of. It sits in the header looking outward at the approach, and when it sees movement it issues the open command. Most are microwave radar, which is why they see through rain but can also be triggered by a plastic bag blowing past.
Motion sensing has one blind spot that matters enormously: it only detects things that move. Stand still in the opening and, as far as an activation sensor is concerned, you have ceased to exist.
Presence sensors stop it closing
That blind spot is precisely why the second family of automatic door sensors exists. A presence sensor looks straight down at the threshold and detects that something is there, moving or not. While it sees you, the door will not close.
This is the safety device. A door running on activation sensing alone will eventually close on a person who paused to answer their phone, and that is not a fault you discover gradually — you discover it the day someone is hurt.
Why the two fields overlap
Look at the plan view above and note that the zones are not neatly divided. They overlap across the threshold deliberately. If the activation field stops before the presence field starts, there is a strip of floor where a slow-moving person is invisible to both automatic door sensors at once. Commissioning is largely the work of making sure that strip does not exist.
This is also why sensors are not a DIY adjustment. Nudging a radar head to stop nuisance opening can quietly open a gap in the safety coverage at the same time.
Reading the symptoms
Most faults announce which sensor is responsible, if you know what to listen for.
Two of these deserve emphasis. A door that opens on its own repeatedly is usually a motion sensor seeing a reflection, moving rain, or traffic passing outside — irritating and expensive in conditioned air, but not dangerous.
A door that closes on people is a different category entirely. Take it out of service. A failed or misaligned presence sensor is not something to leave until month-end, and any competent technician will treat it as an emergency.
Where automatic door sensors sit in the wider system
Automatic door sensors are one input among several. The same entrance may also take a command from a push plate, a reception release, or a card reader — see automatic door access control for how those integrate. Crucially, none of them override the presence sensor. Being granted access does not make the opening safe; the safety sensing keeps control of the threshold regardless of who was let in.
On our own operators, the MC-125 and MCW-100, activation and safety devices are commissioned together and tested as a set before handover.
Keeping them working
Automatic door sensors drift. Vibration moves them, cleaning knocks them, dust and cobwebs sit in front of them, and sunlight angles change with the season. This is a large part of why planned maintenance intervals exist — a sensor check is quick, and it is the difference between a door that works and a door that is quietly unsafe.
Older entrances are worth a specific mention. Safety expectations have moved on, and an aged presence sensor can pass a functional test while still leaving a gap a modern unit would cover. That is the most common reason we recommend upgrading automatic door sensors rather than repairing them again. Requirements for powered pedestrian doors in South Africa are published through SABS.
Automatic door sensors on an escape route
Sensors and escape-route duty are separate requirements, and it is worth not confusing them.
Automatic door sensors keep people safe while the entrance is powered and working. They do nothing at all once the power is gone.
That is why an opening on a fire escape route must also be passable without power, through break-out panels or a fail-safe release. No sensor package substitutes for that.
If you are not certain which arrangement your entrance has, establish it now rather than during an evacuation. It is a specification detail that is easy to confirm and impossible to improvise.
A reasonable maintenance routine
Wipe the lenses with a soft cloth, never a solvent, as often as the environment demands. Weekly in a butchery or forecourt, monthly in a dry office.
Walk-test the full opening afterwards, including the edges.
Re-check coverage after any change to the area around the entrance, because that is what most often puts a working installation out of adjustment.
Automatic door sensors, answered
What is the difference between a motion and a presence sensor?
Motion sensors detect approach and open the door. Presence sensors detect someone standing in the opening and stop it closing. One is convenience, the other is safety.
Why does my automatic door open when nobody is there?
Almost always the motion sensor: a reflection, rain, or traffic moving within its field. It usually needs the field narrowing or the angle adjusting.
Why will my door not close?
Something is in the presence sensor field, or the sensor is dirty or faulty. Check the threshold is clear before calling it a breakdown.
Can I adjust the sensors myself?
We would not recommend it. Reducing nuisance activation can open a gap in safety coverage at the same time, and that gap is invisible until someone is caught.
Do automatic door sensors work in the dark?
Yes. Radar and active infrared do not rely on ambient light, though dirt, cobwebs and heavy condensation affect them.
How often should sensors be checked?
At every planned service, and immediately if the door shows any of the symptoms above. Sensor checks are quick and they are the highest-value part of a maintenance visit.
If your door is behaving oddly
Tell us what it is doing rather than what you think is wrong — “opens but will not close” and “closes but reopens immediately” point at completely different automatic door sensors, and saying which one usually means the technician arrives with the right part.
Report a fault, or request a quote for a sensor upgrade.
The two jobs automatic door sensors do
Almost every fault we attend traces back to confusing these two, so it is worth being precise.
The activation sensor is aimed outward at the approach. Its job is convenience: see someone coming and open in time that they never break stride.
The presence sensor is aimed downward into the threshold. Its job is safety: detect a person standing in the opening and refuse to let the door close on them.
They fail in opposite directions, which is the useful diagnostic. A failed activation sensor gives you a door that will not open. A failed or confused presence sensor gives you a door that will not close.
How each technology actually works
Microwave motion sensing emits a radar field and reports movement within it. It is excellent at seeing someone walking towards the door and blind to someone standing still.
Active infrared emits beams and reads what comes back. Because it detects a stationary object, it is what presence sensing is built on.
Combined units put microwave activation and infrared presence in a single housing above the opening, which is the common arrangement on commercial sliding entrances.
The limitation worth remembering: microwave alone cannot hold a door for a person who has stopped. Any specification offering activation sensing only has left out the safety layer.
Walk-testing automatic door sensors
A walk-test takes about a minute and finds most developing faults weeks before they become failures.
Approach at normal pace. The door should start opening early enough that you never slow down.
Then approach slowly, because weak activation coverage shows up on a slow approach first.
Then stand still in the opening. The door must hold. If it begins to close on you, the presence detection is the problem and it is a safety issue rather than an inconvenience.
Then walk the full width, including the edges. Testing only the centre line is how half an opening goes unchecked for years.
Why automatic door sensors drift
Sensors rarely fail outright. They drift, and the drift is almost always environmental.
Dust film, insect nests and cleaning residue on a lens all read as a permanent target. Condensation in chilled areas does exactly the same thing. In butcheries and kitchens, airborne fat films optics faster than dust does.
Physical knocks change alignment, often from a trolley or a ladder rather than anything dramatic.
And shopfitting changes the field. A display stand, a seasonal promotion or a queue barrier placed into a detection zone turns a correctly commissioned entrance into a nuisance one. That is a setting problem, not a fault.
See automatic doors for business for how this plays out in butcheries, forecourts and cold rooms specifically.
What good sensor coverage looks like
Presence detection across the full opening width, not a single beam at the approach.
Activation range set so the door opens early enough for someone walking briskly, without triggering on passing traffic.
Fields re-checked whenever the area around the entrance changes, and cleaned at every service.
And obstacle detection behind both of them as the final layer: a panel that meets resistance should stop and reopen rather than push through.
When a sensor genuinely needs replacing
Clean and re-align first. That resolves the large majority.
Replace when the housing is physically damaged, when water has entered and corroded the board, or when the unit is obsolete and cannot be configured to the coverage the opening needs.
Sensors are generally configurable to most automatic door brands, so a sensor fault rarely forces a whole-entrance decision. See automatic door spare parts.
Related guides
Automatic door sensor not working covers fault-finding in detail. Automatic door not opening and automatic door not closing cover the two symptoms sensors most often cause.
Automatic door sensors, answered
How do automatic door sensors work?
An activation sensor watches the approach and signals the controller to open. A presence sensor looks down into the opening and holds the door while somebody is standing in it. Most entrances use both.
What is the difference between motion and presence sensors?
Motion sensing, usually microwave, detects movement. Presence sensing, usually active infrared, detects a stationary person. Motion alone cannot hold a door for someone who has stopped walking.
Why does my automatic door open on its own?
Something is moving or sitting inside the activation field. Traffic outside, a hanging sign, or a display that shifts in a draught will all trigger it.
Why does my automatic door stay open?
A presence sensor reading a permanent target. A new display stand, a queue barrier or a poster placed in its field is the usual cause.
Can automatic door sensors be adjusted?
Yes. Field width, depth and sensitivity are all adjustable, and they need re-checking whenever the area around the entrance changes.
Why do automatic door sensors fail in winter sun?
Low sun straight into the optics swamps the receiver. A hood or a few degrees of downward tilt usually fixes it.
How often should sensors be cleaned?
At every service, and more often in butcheries, forecourts and cold rooms where fat, dust or condensation films the lens quickly.
Should I ever disable a faulty sensor?
No. Taping over a safety beam to keep an entrance running removes the protection the sensor exists to provide. Isolate the operator instead.
Do automatic door sensors work on other manufacturers doors?
Sensors are generally configurable to most automatic door brands. We service and supply sensors for equipment we did not install.
How do I test my automatic door sensors?
Approach at normal pace, then slowly, then stand still in the opening, then walk the full width including the edges. The door should open early and hold while you stand.
In short
Automatic door sensors at a glance
- Automatic door sensors are quoted against the opening we measured, not a catalogue price.
- Ask about automatic door sensors and we confirm the opening, the head and the power position first.
- Automatic door sensors are installed and commissioned by our own technicians.
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