Anyone who connected a regular "old" doorbell to OH?


I have an Elcom (Hager) doorbell / intercom and would like to connect it to openHAB.
Anyone who did such a project already?
Thanks in advance.

Any other suggestions are welcome as well.
(I cannot change the doorbell at the door though because it’s in an apartment house).


A simple technique is to adapt a door sensor which uses a magnet and a reed switch. Normally, closing a door moves a magnet on the door close to the sensor on the frame, magnetises two metal strips in a glass vial, which closes the circuit and triggers the sensor.

Inside a ‘ding-dong’ doorbell is a basic solenoid - press the button, the coil energises and a rod which hits two metal bars. The solenoid also produces a wider magnetic field, which is enough to reliably trigger a Z-Wave door sensor next to the coil.

I simply added a Z-Wave Fibaro FGK-10x inside the ding-dong doorbell and reconfigured the sensor to normally open.

To keep the sensor isolated from doorbell voltages you could wire a relay or even opto-coupler in parallel with a bell and the switch contacts to a door sensor. Most UK doorbells are 8-12v AC, which is not ideal to interface with 3.3v, 5v, or 12v sensor inputs.

A door intercom is a lot more complex, as it is likely to use 2 or 4 wires for the bell, audio and power. Reliably detecting a door bell push will need a lot more experimentation to work out what happens across which wires. I’ve seen systems with different number of doors or intercoms use very different circuitry (e.g. bpt, Fermax, etc).

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I have connected my ancient doorbell to openHAB using less then $10 of hardware:

  • sonoff basic
  • programming tool

Re-using the old doorbell button and the bell itself. I have placed the sonoff in-between button and bell transformer, receiving updates in openahb when someone rings the bell. Next to that I have a switch in openhab that sets if the bell should ring or light should flash someone is at the door. A notification is send to the openhab app too…

Apartment style door intercoms have more in common with telephones.
These threads have ideas

Do you mind sharing a few more details about your hardware configuration (connections)?

I was thinking about doing the same, using a Sonoff TH 10, but I didn’t think it would work as the Sonoff requires an input voltage in the range 90-250VAC (according to specifications), and I am pretty sure my bell transformer is nowhere near that - probably more like 18-36 VAC.

You might be interested in this device

Finally I had some time to create this:

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Thanks a lot for your detailed description. I see now that you put the Sonoff at the “high voltage side” (230VAC) of the transformer - clever!

The examples I had seen before yours, put the “smart relay” at the “low voltage side” of the transformer, so I was kind of stuck in this mode of thinking.

Quite a number of other examples that I have seen are only focused on the sensor part (i.e. detecting and reporting" a button press). I very much like the idea of being able to de-couple the actuator part (i.e. the ringing of the bell) from the sensor part.

Given that I have a box of Sonoff’s laying on the shelf, I think I know what my weekend project will be, :slight_smile:

Thanks a lot for all your detailed responses.
As I have some kind of intercom (no video) from Elcom one of the intercom suggestions might fit.
I just need some time to digest it ;-).

Again, thanks a lot for your help.

Check out this thread:

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I need to revive this tread.
The sonoff won’t fit in my case, because I dont have mains of 230V nearby.

Currently I think about an ESP8266-based approach…

If you need to run it on batteries: won’t work for long. A couple of days, maybe one to two weeks depending on the amps of the battery.

What about the Fibaro Zwave Universal sensor:
Just two wires coming from the bell, inside the house you can use a power supply.
Works great for me.

Hmmm, wouldn’t it be possible to power it through the Intercom itself?

I’m using a similar setup, but with a fibaro door window sensor. The drawback with the universal sensor is that it is not zwave+.

Fibaro has released new.module with zwave+ that would work just as well.

If I would go this approach today I would probably modify a zigbee aqara door sensor

Regards S

Yes, of course. If you have 3.3 or 5V DC available, depending on the esp8266 module you are using.
If the voltage is a higher DC voltage you could use a step down converter:

Because of range? I’m using a lot of mains powered zwave devices. so even outside my house there are no range problems with zwave non-plus devices, thanks to mesh.

Thx, hadn’t noticed yet.

Since the universal sensor is relaying, it will downgrade any zwave+ passing through it to plain zwave. Probably isn’t a problem, but last time I reset my zwave network I made decision to have all relaying components as zwave+.
Zwave+ is supposed to have a bit lower latency, not sure it is noticeable. I don’t have any range problems, same as you I have a fair amount of zwave nodes.

I’ve heard about this but not found a “good” source yet to verify.
I have a mix of non-plus and plus and no problems at all :grinning:

Yeah hard to find sources. Without referencing to technical specifications, it is mostly blogs and similar. Some info here:

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