Why locks with master pins are a bad idea, and how can you improve your home security
A master key lock is a pin-tumbler lock that allows the lock to be opened with two or more different keys. This is what’s typically used for door locks in buildings with many tenants, such as apartment complexes, office buildings, hotels, and storage facilities. All the occupants are given a key that unlocks only their own door, called a change key. The master key unlocks all the doors in the building.
Master pins are used to pin up locks so that a master key will work as well as a change key. In a school, for instance, the janitor will have a master key that will work for all the classrooms, but each teacher will have a change key, which functions only for a particular classroom. There are also subordinate master keys, which, for instance, open every room on a dorm room floor. Furthermore, grand master keys will open all the rooms in an entire dormitory or office building. Finally, a great grand master key will open all the doors for a whole campus, or every office in a commercial building complex. The higher you go, the more complicated it gets; but in general, the pin stacks in the lock have multiple key pins and master wafers above the key pins, which allows several different keys to work in one lock.