Dr. Smart Home Puts Apple Presence on the KNX Bus

A Sensor Without a Sensor. Because Why Not.

Let me be clear from the start: this is not a story about KNX presence sensors being bad. They're great actually. They can detect actual presence, not just movement — you can sit still reading a book and they'll still know you're there. Technology has come a long way.

But here's the thing. Doctor Smart Home already has iPhones in the household. He already has HomePods. Apple Home already knows who's home and who isn't — it tracks iPhones via geofencing, WiFi, proximity to home hubs, and probably some other Apple magic that nobody fully understands.

And guess what. Apple already solved this problem — at least halfway. They have all the data. They have the infrastructure. They just haven't made it easy to get that information out of Apple Home and into something more useful. Like, say, a KNX system.

So the question became: can that presence information be pulled into KNXwithout buying another sensor?

Spoiler: yes. Kind of. With caveats. Let me explain.

The Core Problem: Apple Home Can't Update Sensors

Here's the issue. In Apple Home, you can set up an automation that says "when nobody is home, turn off this light." But you can't say "when nobody is home, set this sensor value to 0."

Apple Home automations can control devices — lights, plugs, switches. They can't write to sensors. Sensors are read-only from Apple's perspective.

So Doctor Smart Home did what any reasonable person would do: he created a fake socket and let Apple Home flip it.

Creating the Virtual Socket

In 1Home, a new device was created: "Presence Apple Home" with type Socket: On/Off. Two group addresses assigned:

  • 12/1/1 — On/Off Set (DPT 1.001)
  • 12/1/2 — On/Off Status (DPT 1.001)
A virtual KNX socket in 1Home

This device doesn't exist in ETS — it's purely virtual. The group addresses are just sitting there on the bus, waiting for someone to write to them.

1Home device configuration showing the virtual presence socket

Using 1Home's Matter Bridge, the socket was exposed to Apple Home. After pairing, it appeared in the Home app like any other smart plug — which is exactly what we need, because Apple Home automations can control plugs.

Then, two automations in Apple Home:

  1. When the first person arrives home → Turn "Presence Apple Home" ON
  2. When the last person leaves → Turn "Presence Apple Home" OFF
Automations in Apple Home can control devices but they can't force values to sensors

These are the built-in presence triggers that Apple provides. Simple enough.

The Missing Piece: Why the Graph Stayed Flat

Here's where things got stuck for a while. When Apple Home sent the "turn on" command, the KNX bus monitor showed it arriving on group address 12/1/1. But 1Home didn't update the device state. The graph stayed flat. Nothing happened.

The reason? With a virtual device, there's no physical actuator to respond with a status update. The Set GA (12/1/1) gets written, but the Status GA (12/1/2) stays empty. 1Home is waiting for a response that never comes.

The fix: a simple 1Home automation that mirrors Set to Status.

  • Trigger: When 12/1/1 changes
  • Action: Write the same value to 12/1/2

Now every command from Apple Home gets properly reflected in 1Home's device state. The graph finally moves.

KNX Bus Monitor showing the Set and Status telegrams

Making It a Proper Sensor (Because the Socket Felt Wrong)

At this point there was a working solution. But the socket device type was annoying. It doesn't show up in the sensor bar in the 1Home app or on 1Home Touch. It's a socket. It looks like a socket. It feels wrong.

So one step further: another virtual device — this time an Occupancy Sensor — with group address 12/1/3 for "Occupancy detected."

The mirror automation was updated to also write to 12/1/3 whenever 12/1/1 changes.

The "mirror" automation in 1Home

Now there are two devices:

  • A socket (hidden away in "Utility" — the imaginary room for system devices, like the cooling mode switch from the HVAC setup)
  • A proper occupancy sensor (sitting proudly in "Entrance" where it belongs)

The socket does the work. The sensor gets the credit. Just like in real life.

Does It Actually Work?

Honestly? At first, it didn't.

The whole family left the house. Walked far enough that Apple should definitely notice. Checked the graph. Nothing. The sensor stayed "home."

All the location settings were rechecked on both phones. Everything was already configured correctly. Doctor Smart Home was about to give up and write a strongly worded forum post about Apple geofencing being useless.

And then... it just started working.

Here's the graph from a recent hike:

Presence graph showing On until 12:05, Off until 13:35, then On again

You can clearly see:

  • Home (On) until around 18:05 — everyone was home
  • Away (Off) from 18:05 to 19:15 — out on a hike
  • Home (On) again at 19:15 — back from the hike

So yes, it works. How well it works over the long term? We'll see. This article is about the hack itself, not about long-term reliability testing. Doctor Smart Home will probably try controlling some things based on this signal — A/C, lighting, media. Maybe there will be a follow-up article. Or maybe some other hack will come along and this one will be quietly forgotten. Everything is possible.

The Caveats (Read This Before Getting Too Excited)

Let's be real. Nobody should bet their salary on Apple detecting presence with 100% accuracy. Here's why:

People without iPhones don't exist (to this system). If the kid has an iPad but no phone, Apple thinks nobody's home when you leave them with a babysitter. Same for guests, parents visiting, anyone whose iPhone isn't paired with your Home.

What if everyone's phone is dead? Apple will think you left. The heating will turn off. You'll sit there in the cold wondering why you trusted a blog post.

Geofencing is... geofencing. It's not instant. It sometimes takes a few minutes. It might fail silently. The internet is full of people complaining about Apple Home presence detection being unreliable — and they're not all wrong.

Could this be done with WiFi detection instead? Probably. Some people track phone MAC addresses on their router. That would work even on mobile data... actually wait, no it wouldn't. Hmm. The hope was that Apple would detect you even on mobile data (via geofencing), but that hasn't been thoroughly tested yet. More research needed.

Bottom line: This is a cool hack. It's free if you already have Apple devices. It's fun to set up. But maybe don't use this as your only input for anything safety-critical. Trust, but verify.

Tips for Making It Work Better

If you're setting this up, here's the checklist:

On all iPhones in your household:

  • Settings → Privacy → Location Services → Home → Always + Precise Location
  • Settings → Privacy → Location Services → System Services → HomeKit enabled
  • Settings → [Your Name] → Find My → Share My Location ON

In the Home app:

  • Home Settings → People — verify everyone shows with location sharing enabled

On your home hubs (HomePod/Apple TV):

  • Restart them after iOS updates (seriously, this fixes a lot of weird behavior)

Remember: Only iPhones and Apple Watches count as "people." iPads, MacBooks, Mac Minis — none of those matter. So if the kid is watching cartoons on the iPad while everyone else is out, Apple still reports "nobody home."

Have you tried something similar? WiFi-based presence? Router MAC tracking? Something even weirder? Let me know in the comments — or tell me why this is a terrible idea and I should stop immediately.

Dr. Smart Home out.