This happened several years ago and is the only ghostly encounter I have ever had, but I still don't know how to explain it.
My husband and I were renting a house. The bedrooms were located off a small hallway and the hallway had a door that led to the den, as well as a door that led to the living room. Both of these doors as well as all three outside doors had those old fashioned sliding metal bolts on them to lock them. It was a nice secure feeling knowing that when we went to bed and locked the hallway doors, an intruder who came in to the main living area of the house would not have access to us in the bedrooms.
Well, one night my husband went to bed before me. He was always kind of bad at making sure the house was locked up, so I was checking the doors before I went to sleep. The sliding metal bolt on the door that led from the living room to the breezeway was not locked and I remember being annoyed with my husband and thinking that, as the man of the house he really should make sure these things are taken care of. I locked the door and went to bed a little angry, intending to speak to him about it in the morning.
Well, as it happened, I was up before him the next morning. When I went out to the living room, the sliding metal bolt on the door to the breezeway was back in the unlocked position. I couldn't understand it. I distinctly remembered doing it the night before, all the while complaining to myself about my husband.
I also used to hear "footsteps" when I was alone in the house, but I put that down to the old wood floors creaking but the door being unlocked... That I have yet to explain.