First off there is a mod made by Ldones called Night time door locks...you can find it by googling it.
However there's issues with it from what ive read and this mod is very old(old school) but before the issues came to bare it was a fine mod.
Doors of merchants and residents were locked at night and unlocked in the morning,churches and ale houses stayed unlocked.
I feel this mod would add a alot of realism to the game and would be easy to implement.
So hopefully someone will take up thereins on this mod.
Yourd truly,
qwert
ps- different doors would better locks than others....merchants locks would be better than residents and so forth.