We have a building with one of those phone keypads in the vestibule that calls a residential phone number. The answerer can then chat with the caller and then can buzz them in by pressing a key combination into their keypad.

We need to upgrade this system. I can figure out how to do the dialing part, but how do I watch for the tone combination from the tenant in order to activate the door lock - and what do I use to activate that door latch?

Any references out there on this type of project?

Michael