Your doors look quite flexible with respect to messages, you just need to have a two-way door option and you need to be able to get and set the open and locked properties. For example, a door can be locked (to prevent it being opened), but it is unlocked by using a swipe card, not a key. In fact, this might be an example where unlocking and opening happens at the same time, so you need to be able to set the open property and clear the locked property when you SWIPE CARD. Oh, and you need to be able to customise the description so that you can say whether the door is open or closed within the description. This means you need to be able to get those properties.