I moved into an apartment complex where the key is both unique to each apartment door, but every key can open the front door, how are both possible?

Question

I moved into an apartment complex where the key is both unique to each apartment door, but every key can open the front door, how are both possible?

In: 986

Answer 1

Is called Maison keying. I do not and have not seen it very often in my area. Mostly in campus Dorms. That have multiple rooms that share a common entry door.