I live in a studio flat, one of several in a large house. The entrance to my flat has a 5 lever lock. I have a key. The landlord’s handyman also has a key. Some while back, the tenant of one of the adjacent flats became suspicious that the handyman was entering his flat, and generally poking around. So he installed some kind of secondary lock. As I recall, it took the form of a device that once he, the tenant , unlocked the main lock of the door from the outside, he could then open the door a few inches…, this gave him access to the next lock which had a stout chain. He could then unlock the secondary lock with the key for that.
My question is… does anyone know what this is actually called, so that I can research a bit further.
I’m slightly suspicious of the handyman, but don’t want to start chucking accusations around without specific foundation ( the other tenant moved away, took his lock with him, so I can’t ask him ). The idea is that I can install this secondary lock, the flat will be secure, and yet the secondary lock will not be obvious from the outside of the door.