We have a gate in a city with an intercom button on it. When guests push the button, it rings upstairs, and then we can talk with them or let them in with the press of a button. The button appears to release the latch plate on the gate.
I want to replace this with either or both of a keypad or a smartphone-operable system.
What should I search for? What product category is this? How do I discover what might be compatible with the existing system? I am struggling to know what to search for.