When I moved into my new apartment last summer, my landlord gave me 3 keys; one for the front door, one for my unit, and one for my mailbox. So say my unit is one of 32 – if all 32 units have just one person living there, that’s 96 keys. Of course, most of us have family or roommates who also need keys, so this number is quickly climbing to a few hundred. Now manufacturing, maintaining, and potentially replacing that many keys sounds like a lot of money and a lot of hassle. But it’s unavoidable, isn’t it? Not quite – in fact, you could narrow that down to one key per person with the right set of locks.


Before we talk master keys, we need to establish some lock basics. In the most basic terms, locks are little puzzles on the interior, and the correct key will arrange the pieces in the right pattern so that it opens. My doors (and probably yours too) have cylindrical locks – super standard stuff.

lock 1


The lock will have a few chambers that correspond to the notches in your key. Each chamber has a pair of pins in it: a driver pin, which is a standard size, and a key pin, which will be different in each chamber. The correct key pushes up the key pins so the drivers all line up above an invisible line called the shear line. This creates a gap in the lock so the key has room to turn.



When a lock is fitted for a master key, it’s built so that the puzzle has multiple solutions. An additional pin called a master wafer is added to the stack in a chamber, creating additional space between the driver pin and the key pin. With the addition of this little hockey puck, we’ve created another pattern that opens the lock. So if Key A pushes the pins so that the master wafer is above the shear line, Key B will push them so the wafer is below the shear line. The lock will accept either of these as valid solutions and open just the same, since all the driver pins still end up above the shear line, and all the key pins are still below.


lock 3

unlock keysThe more wafers you add, the more combinations of pins will open the lock. So going back to our diagram, if we put a wafer in each of the 5 chambers, our lock would open for any of 32 possible combinations. Applying that to life, the front door of my building could have 32 different keys that all open it, but which also function as an individual key for a tenant’s apartment. Furthermore, if the lock on my apartment was a twin to the lock on my mailbox, I could replace my three current keys with one.

So why did my landlord give me three keys?




The thing is, the more keys can open a lock, the more ways there are to pick it. With this set up, if someone wanted to break into my building, they don’t have to figure out the one pattern that opens this lock, they just have to find the easiest of 32.

One of the biggest rules of general security is that as something becomes more convenient, it also becomes less secure. It’s the same reasoning behind why you’re supposed to use different passwords for all your online accounts. So having all the keys I do may be less convenient, but it means the coupons and credit card offers in my mailbox are that much safer.

pexels photosThis isn’t to say that master keys are an inherently bad idea. The thing you have to consider here is scale. If you want to get a lock that opens for 4 keys, that’s probably fine. Yeah, it’s not as secure as a one-key-one-lock setup, but it’s certainly more practical than a 32-key lock. Furthermore, most thieves don’t actually pick locks – they’re way more likely to steal a key or break a door, since it’s quicker and easier. So there are a lot of sides to this debate. If this is something you’re considering, call now and we’ll get you set up with a system that best meets your needs.