A master key system is a key plan in which selected keys can open a number of predefined doors. It improves control, reduces key replacement costs, and is convenient because fewer keys are in circulation. It also provides quick access to all rooms within the premises, e.g. for security staff and management personnel. This is not only convenient but can also save lives in an emergency. In the example to your right, the ‘Master Key’ would open all doors and lock types in the property and is held by the caretaker. The Sub-Master A opens the main entrance and all the locks on the ground floor, and is held by the manager of the company that occupies that floor. The same applies to Sub-Master B. In addition, each employee has one key that opens the main entrance, their own office door and their filing cabinets. These keys work with different types of locks, e.g. door locks, cabinet locks, padlocks, etc., as long as the cylinder inside them is of the same model.