Here is a demo video of this project!
This is a code for a device placed near the door which can unlock the entry door over the button for unlocking on the interphone. For opening the door I used a servo motor because I couldn't simulate the door opening button press by soldering the wires on the button pins inside the interphone. It also uses Telegram for communication between ESP8266 and a smartphone, and supports multiple users.
If you want to use this sketch, feel free to copy, modify it, and so on.
I am a beginner in the embedded world and if you are too, and you want to learn from my projects, I write a lot of comments so you can easily follow the code.