I have NEVER encountered a doorlock in my dream that worked. I thought it might be a good RC. Go to a door that’s supposed to be locked and see if it is, or lock a door and see if the lock works.
Good point, a door that can’t be locked it a major part of a recurring nightmare for me. Doing a RC using door locks couls actually help with recognising this nightmare. I’ll give it a try 
That’s odd. I’ve never seen(or heard of) a locked door in a dream.
But it sounds like something to try someday. It just might work. 
Suppose you forgot about some working lock! Well. I can’ät remember any working lock either. i only remember one that was supposed to be locked in a LD. I conjured a key that proved unnecessary. Good observation.