Ring and a bunch of these devices are convenience machines. The doorbell itself at minimum has a microcontroller, camera and mic with WiFi access, the server controls the doorbell, stores footage and makes live feeds available over the Internet for when you are away from home, a phone app lets you see who is at the door and let them in even when you're not home.
For anyone interested, a self-hosted home assistant will get you 80% of the way there, depending on how paranoid you are you can also set up POE cams and frigate.
Or just have a pot someone can bang really loud that works too.