A new project has turned the Raspberry Pi into a cheap electric strike. The project uses facial recognition to make it particularly easy to open the door and should also be comparatively easy for beginners to realize. Also, relatively little material is required.
https://www.notebookcheck.net/Raspberry-Pi-Turn-the-single-board-computer-into-a-door-opener-with-face-recognition-and-SMS-alert.460146.0.html