For our Smart Lock, we will be using a servo to lock and unlock the door. This is not really how most of these devices work, but it will do the job for this mini smart home.
You will want to connect this servo to Servo 1 on the Crickit.
To allow for the servo head to stick out through the door frame, I cut a hole in the wall next to were the door opens. Then you will want to attach the servo to the inside of the house so that the servo head stick outside next to the door. Attaching one of the servo arms will let use lock the door when needed.
You will want to be sure to change the servo arm position so that it is horizontal when the door is locked and vertical when unlocked.