I’ve been mulling about this for a while. I guess it depends on the particular door and how the interior lock mechanism works…
I’m imagining a push/pull actuator either mounted on the inside of the door connected to a two channel relay, powered by around 5-7 volts, or possibly on the back side of the frame, manipulating the lock “catch” up or down.
If I ever get going with the project, I’ll make a thread for that.
But there are a few threads on here that might be of interest (probably more)