My dorm has a card reader on the outside of the building, then an old fashioned key for the room. This, to my lazy ass, was very irritating. I had to make something to make things easier. I initially wanted to add the card reader to my door so I could use the same card to enter the building and my room.
Plans changed, my RFID scanner never came, so I came up with something better. I used Node.js to create an express server on my raspberry pi and created an Android App to communicate with it. I then bought a servo motor, and after countless trial-and-error with a friend 3D printing an arm to fit my door lock, was able to set up something functional.