Detecting Pressed Call Button on Video Intercom with ESP8266

Hi,


DOMOFON
1. video
2. VCC
3. GND
4. chime (4.5v) - short-circuits to ground when pressed.

I'm looking for hints on how best to solve the status detection problem.
I have a video intercom where 4 wires go. I wanted to detect pressing the bell and sending data over the mqtt further. I found 2 wires that short together when someone presses the bell only question arises.

I want to detect this from another chip (ESP8266), on 2 of these wires I have 4.5v with a multimeter I measured that the button simply short circuits the state line to GND.
What is the best way to detect a low state from an Arduino or similar?
I have a couple of ideas.
- transistor on the line esp
- measuring the voltage on the line analogue
- a common ground and a resistor to check the high state.

Please direct me on the right track.

Optocoupler. There is probably also an audio signal on 4 and shorting it to anything will distort the conversation. Additionally, there will be full galvanic isolation between the devices.

If the button is short-circuiting to ground and sound is flowing through there during a conversation, it is a good idea to detect the button press with a circuit with a high input impedance and a low-pass filter (which does not pass sound) at the input. You have an example of a mosfet solution here:

.

simulation .