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Security & Safety · 9 November 2026

The intercom opens the gate. What does the lock do when the power goes?

The intercom opens the gate. What does the lock do when the power goes?

Most of what I read about smart entry is about the clever part. The face on the intercom screen, the unlock button on the phone, the visitor snapshot when nobody answered.

Very little of it is about the dull part: what the door does when the power is off.

That question is not answered in ETS. It is answered at the supplier, the day somebody picks a lock off a shelf. And in a country where the lights still go out, it is worth asking before the door is hung.

KNX does not own the intercom

Start with what KNX is and isn’t doing here. A KNX Association article on adding door intercoms to a KNX offer is blunt about it: technically, the door intercom is not part of the KNX ecosystem, except for its presence on the user interface. The intercom is its own system. KNX sits beside it.

The pieces that connect them are ordinary. A touchscreen can show the video feed. A volt-free contact can trigger a gate, a bollard or a lift, with “a bit of local wiring”. SIP carries the audio and video to third-party panels.

2N is a good example because its integration page is specific. An event on the intercom sends an HTTP command to an intermediary device, which turns it into a KNX group address telegram. That can flash lights, set a “Do Not Disturb” scene or raise an alarm. Going the other way, KNX can drive the intercom’s relay outputs. It needs a KNX/IP gateway or a logic server to bridge the two, and the page lists door lock control among the features.

One thing that page does not say is how relay, lock or door status gets reported back to KNX. I could not find it, so I won’t guess. If you want the house to know whether the door is actually locked, that is a question for the supplier before you buy.

The lock decides, not the programming

Now the dull part. Allegion’s explanation is the clearest I found.

Fail-safe means the door is unlocked when power is removed. Power keeps it locked.

Fail-secure means the door is locked when power is removed. Power unlocks it.

Both terms describe the secure side of the door, the outside. And they are properties of the hardware, not settings:

  • Electromagnetic locks (maglocks) are fail-safe only. Take the power away and the magnetic bond is gone.
  • Electric strikes come either way, and fail-secure is the usual choice.
  • Electric latch retraction hardware is fail-secure only. The latch projects when power goes.
  • Electromechanical locks and electrified panic trim come either way.

No amount of clever KNX logic changes this. If the lock is a maglock, the door opens when the supply drops. If it is a fail-secure strike, the door stays locked, and the person outside stays outside.

Two ways to get it wrong

Fail-safe at the front door is a security problem. Allegion puts it plainly: a fail-safe door is unlocked during a power failure, which is a security risk. That is why fail-secure is the more common choice, along with power consumption. On a Johannesburg front door or gate that goes down every time Eskom does, a maglock on the outside is an open invitation.

Fail-secure on a door someone needs to leave is a safety problem. A fail-secure lock on an escape route can trap people. The Axis write-up says fail-secure doors need a mechanical override on the inside, a handle or a crash bar, and that this is a legal requirement in most jurisdictions.

Most hardware allows free egress either way. Maglocks are the exception. They need release devices, and if a sensor triggers the release it has to also release on power loss, on a push button by the door, and on fire alarm or sprinkler activation.

So the sensible domestic answer is usually a fail-secure strike on the entry side, with a handle that always works from inside. The pattern I would hold up as correct is the one the Axis article describes for commercial buildings: secure on the way in, free on the way out.

What I did not verify

The codes quoted in those sources are mostly American, NFPA and similar. They are not South African regulations. I have not checked what SANS or a local fire officer requires for a given building, and I am not going to pretend otherwise. For fire doors, escape routes, and anything in a commercial or multi-unit building, confirm the requirement with the building’s fire consultant. The physics of the lock types applies everywhere. The rulebook does not.

What to ask before the door is hung

For anything with an electric lock, I would want these written down in the spec:

  • Fail-safe or fail-secure, stated for every electrified door and gate. Never left as “whatever the contractor has”.
  • A mechanical way out. Handle, thumb-turn or crash bar, that works with the power off.
  • A mechanical way in. A key cylinder that works with the power off, and a spare key somewhere that isn’t inside the house.
  • What the power supply does in an outage. Is it on the backup circuit? For how long? If the lock holds only while a battery lasts, the owner should know the number.
  • What the intercom and gate controller do when the mains returns. A door that unlocks itself as the supply comes back is a failure too.
  • What KNX is told. Does the system know the door is locked, or does it only know it sent an unlock command? These are different things.

None of that is expensive. All of it is cheap before first fix and awkward afterwards.

Test it with the owner watching

At handover, turn the supply off and try the door. From outside, with the key. From inside, without it. Walk through what happens to the gate, the intercom, the keypad. Then turn the supply back on and watch what each thing does.

It takes ten minutes, and the owner learns the failure behaviour once, calmly, instead of at 8pm in the dark.

What I’d say to an architect

The entry sequence is a design moment. People notice the face on the screen. They rarely notice the lock, until it is wrong.

I am not tied to a brand on any of this. The intercom and the lock are chosen to suit the building. What KNX adds is one place to see and control the lot, as long as the hardware behind it behaves the way you decided it should. If you have a project where the door and gate are still a line on a schedule, it is a good time for a conversation about what the project needs.

wayne@knxlogic.co.za | 082 564 3982 | www.knxlogic.co.za

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