Hello! I'm about to create an arduino / esp32 thingy which sends me an http request or a telegram message (or whatever) when my doorbell is ringing, or in other words when there's current flowing across the 2 buzzer's wires. The chime in my apartment is a 12v Vimar buzzer (Product Catalogue - Acoustic signallings: 12V SELV 50-60Hz bell white - 14370 - Plana - Vimar energia positiva), but I could profit from some guidance on how to get the signal from the buzzer into a gpio without frying the microcontroller.
I've read of "optoisolators" but most of the projects I'm seeing on the web involving optoisolator are about "safely driving external loads" apparently, but I'm not driving anything, I'm only receiving, so I'm unsure what component would fit best and how to wire it. Maybe it's another kind of component.
I'm not talking about software or code, my problem is limited to my lack of knowledge in voltage step-down/up when something in my circuitery is beyond the 3v-5v comfort-zone-range I'm used to. I've used some 220v relays with arduino to control my lights and they're still fine, but this is the other way round really.
Thanks for any hint!
Hi, @rus_pa
Welcome to the forum.
To provide the isolation between your buzzer and Arduino, an Opto-Coupler would probably to the job.
Google;
arduino optocoupler input
You will find many examples that should help.
Tom.. 
PS. I'm off to bed, need all the beauty sleep I can get. 
Surprisingly 100% of the results point to non existing or paywalled pages 
but at least I understood that optocoupler may be the way to go. Thanks!
I get dozens existing normal pages, not a single bad result: https://duckduckgo.com/?q=arduino+doorbell+optocoupler
You should check your computer for viruses, maybe upgrade the operating system and browser, select a better browser, and perhaps a better DNS service with a filter, and select a more normal search engine.
If you don't know if it is AC or DC and don't know the polarity, then you need a full-bridge-rectifier plus a resistor, or else just a single diode plus a resistor before the opto-coupler.
The page I linked clearly states AC current type in the technical data section.
Besides, you would have known that if you took the time to read my question instead of rushing juvenile, baseless IT assumptions and exotic search engines suggestions.
Sounds like this needs to be moved to somewhere such as Bar Sport! 
Bell transformers are typically an UNRECTIFIED transformer in the range of 10 to 16 volts.
This is by its very nature AC not DC.
It could be tapped and then rectified for a better signal using a voltage divider or regulator. (regulator preferred).
Either way it needs to be both isolated and changed to DC before it is easily useful to an Arduino to keep the cost down or prevent damage..
There are small CURRENT SENSORS also available for Arduino's that may be more useful too.
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