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.
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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, 
All,
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:
All,
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:
https://manuals.fibaro.com/binary-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
https://www.domoticz.com/forum/viewtopic.php?t=25490
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:
https://de.aliexpress.com/item/DC-DC-Step-Down-Module-LM2596S-LM2596-3-2V-40V-To-1-25V-35V-Adjustable-Power/32813967853.html
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 
Yeah hard to find sources. Without referencing to technical specifications, it is mostly blogs and similar. Some info here:
The Smart implant sounds promising. I could even implement the buzzer.
Even though it’s more expensive.
Because Iam no electrician, I need to figure our first how to connect it… 
That is not a big problem
You’re the man!
Thanks.
I will order one right away 
Be careful with the electrical configuration.
I, too, am using a Fibaro Universal Binary sensor. It needs 9-30 VDC (DC!) to run.
The Smart Implant seems to be the same (except for zwave+ maybe but connectors are the same).
Doorbell circuits at least in DE typically use 8-12 VAC (AC!). Yeah, strange. Some bell models may continue to work if you apply a different voltage, others may fail (such as mine).
Using that on the input side is fine, but if you also want to keep your doorbell, you also need to provide it on the output side, too (you eventually want to suppress doorbell sounds at times ? so it wouldn’t ring autonomously but only if OH wants it to).
I ended up dropping the bell and now generate the sound via speaker (plus blinking lights, pushover etc, but you will want to hear a sound, too).
