Since I live in a house a ways off from anything except for the much bigger and fancier house in front of mine blocking it, the door is unlocked.
All the time reguardless of whether anyone is home (i.e. I'm paranoid)
The unlocked when someone is home and locked otherwise (i.e. I'm naive)
Never reguardless of whether anyone is home (i.e. I have nothing worth stealing)
The locked when someone is home and unlocked otherwise (i.e. I live in a prison cell))