In the field of locks that offer a multitude of solutions and possibilities:
A single key (the master) opens all the doors you want, each retaining its own key.
Of great use in communities: an owner with one key can open all the doors of your property: the portal, the garage, your own home ... but unable to open the housing of their neighbors.
Forming separate groups, each with its master key, and a teacher who opens all doors. It can be considered as several simple master key acted on a great teacher. Widely used in hotels, hospitals, public schools, etc..
Master key is the most comprehensive type: in this system a master key can open a group one or more doors of different groups. It is used primarily to restrict access based on hierarchies.
Masterkeying modifiable at will
It has a first master key will be changed to the user.
The owner of the premises may vary, as often as desired, validation of the keys in the different gates because they are mechanically identical.
Mechanical Amestramiento + plus security
Combining mechanical master key with the mail, there are added security. A user, no neighbor of the property, you can have a key input in the garage, while the neighbors have keys that are part of the plane mechanical master key for common access, and for access themselves also have electronic security.