Trying to keep control of lots of locks, each door has its own key, but only want to carry one key? We can do that. In a commercial system, a way to think of it may be a 5 story hotel. There is one key that is a master key and opens every door, a second set of keys of one through five, each opening all the doors on an individual floor, and a set of keys that only opens the individual room.
There is a simpler solution that can be useful at home. Sometimes called the “man cave solution”. One key that the family members have that opens the house and separate garage, and a second key that opens only the garage or “man cave”. By having the second key, muddy boots can not tromp through a home.
The image shows a basic master key system, allowing different people to have access to different levels of an office. This allows for better key control to protect sensitive areas.