A new video tutorial, "Door Functionality in Unity", has been released on design3.
"Learn how to implement door logic with Unity's scripting system. First you'll learn how to open the door as soon as a player is in range. Then you'll create logic to require a player to open the door with an action button, or even tounlock the door first. By using triggers, raycasting and enumerations, you can control when and how a player interacts with doors in your game levels."