I wouldn’t recommend this. It just makes it easier for others who don’t need to know (i.e. burglars looking for an easy place to hit) to see if the door is unlocked. Why make it easier for them?
Perhaps a better idea would be to have a widget on the phone that displays the lock status. These are the requests for widgets:
Perhaps included in their implementation would be viewing the lock status along with being able to unlock/lock. You still have simplicity with viewing the status, but in a more secure way.