I work for a small company in a Milwaukee WI. Last year we purchased a large office/plant facility that had been vacated when the previous company built a bigger facility. I am in charge of the computer and phone systems, so I have access to almost all the building.
Now our phone room, or closet, is in one of three separate basement spaces. When we got into the building I did not have a key to the door for this room so it was left unlocked. After about 2 months, I would walk down to work on something and the door would be closed tight and the lock would be enabled. And I would get maintenance to open the door for me. This happened about 3 times before they put a new lock on the door and gave me and one other person the key.
The new lock is always on, so when the door closes that's it. About a month or so after the new lock went on, I would walk town to find the door open, just a crack. After finding out the other person didn't leave it open, and that no one else's key worked the lock, I got a little spooked. This has happened at least once a week. Now in the past month, when I am working in that room I hear a knocking on the door across from the phone room. (Storage Room) I instantly get freaked out and hi-tail it upstairs.
I talked to an employee of the original company, and he could only tell me that one of the founders of the company had died shortly before we purchased the building and had been here when the place was built, but didn't die in the building.