How come Key A can open Lock A. Key B can open Lock B. But not lock A. And key C can open all the locks? Doesn’t that mean A and B should be able to open each other?
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A keyhole unlocks when a specific combination is inserted (usually represented by numbers, but we will use letters). Key A is xxxAx, Key B is xxxBx, and Key C is xxxCx. Keyhole A is configured to accept xxxAx and xxxCx. Keyhole B is configured to accept xxxBx and xxxCx. Here is a video that explains it and provides good visuals [https://youtu.be/8U6rdI_uG2c](https://youtu.be/8U6rdI_uG2c)
If you find this interesting, try watching more lockpicking videos, there are even more interesting things lock makers do 😃
A master key only works on the locks it’s designed to open
When a key is inserted into a lock normally, it raises pins to specific points where they no longer stop it from turning, and most locks have different heights the pins need to be at to unlock making other keys not work
A master key works by each lock having an additional point made on the pins that they can be raised to that also allow it to be rotated, so although they still work individually with their specific keys, a secondary key (the master key) works on them all as well
Inside of a lock are little pins that the key pushes up. These pins come in a bunch of different lengths.
When they are pushed to the right height the lock will open.
Mastered locks/keys have 2 arrangements in which the keys will open the lock (because they use different lengths of pins which allows for multiple combinations).
Imagine all the children in a family have their own bank account with a personal identification number.
But their parents also have a different, single, personal identification number that can can access all the children’s accounts.
So the analogy is that each of a ‘family’ of locks have to be created to allow *two* different keys to perform an unlock. This means the pins in each lock will have one break at a common position and another break at a variable position.
All keys are cut to specific code numbers. Imagine a master key having the key cut to code 76765. All the locks can have their unique variations, but with an added pin combination that totals 76765 (your master key code).
Pins inside the cylinder number in length from 1 to 7 typically, but you can switch pin combinations up to total that master code. Code 34543 for the regular room key, just add master pins (two different types of pins are used for master keys) 42222 and you can have two keys open one lock. With more variances, you just add master pins to all the codes you’ve created to total 76765, and your master key will work with many locks.
Side note, don’t use a difference of just 1. That master pin 1 is so thin and tends to gets jammed.
Think of keys as just mechanical representations of a PIN. You can have a user level PIN and then an admin level PIN. Cuts on a key are just physical representations of these PINs and are usually numbered according to how deep the cut is, 0 being the shallowest, 9 being the deepest.
A lock can be set up to accept any number of different PINs as well as a “master” PIN that overrides all others. This can be set across a number of locks so you have a single key that only opens its own lock, and one key that opens all locks in the system.
Usually, what happens is one key is set up to to be the master with one cut that none of the user keys have. All of the rest of the keys are variations of this master. In a system, ALL of the locks accept the master key and will have a variation off this master key.
For example.
Master key: 1,2,3,4,5
Key 1: 3,2,3,4,5
Key 2: 5,2,3,4,5
Key 3: 7,2,3,4,5
Key 4: 9,2,3,4,5
In this case, the 1st number in the key cuts changes. This lock would be set up to allow its own key + the master key. So, from the example above, Lock 4 would be set up to accept 1,2,3,4,5 AND 9,2,3,4,5 using what it called a “master pin” to change the length of the first chamber stack to 1 and 8 for a goal of 9. Key 2 would need a 1 pin and a 4 “master” pin to make it a total of 5, making the lock work on a cut of 1 or 5.
And after all this, we can also have Maison locks (accepts any keys from the system) and shadow keys (that exist in the system but not on a key). And then there are things like Grandmaster and Great Grandmaster keys for much larger systems.
Oh, and a side note, there are no magic “skeleton“ keys that open all locks, and a Master key from one system isnt going to work as a master key on another…
ELI 5:
To open the lock you must rotate a gear to pull back the bolt.
The gear doesn’t want to rotate because there is a pin that has dropped down a chute and blocked the turn. Push it up out of the way, and the gear will turn.
To lift the pin, you insert a key to push it up and out of the way.
This is what most old style locks were. Simple, but effective for most uses. However this is a very easy to beat lock. Push the pin up far enough and the lock opens. No real challenge.
The solution is to make it so pushing up to far also locks the gear in place. So the locking pin is now 2 pins sitting on top of eachother. Push it up just far enough that the break point is on the border of the spinning section and the stationary section and the key/gear will turn. To far up and the bottom pin binds. Not far enough and the top binds.
This is most modern locks.
Master Keyed locks have 2 breaks. So 3 pins.
The first break is for the normal key, and is unique to each lock. (or perhaps a small set, like “storage closets”)
The second break is identical across all locks in the set, and is the master key. (this would be all doors in the building)
Instead of thinking about a key “opening” a lock, let’s switch to thinking of a lock as “recognizing” a key. Then we can say that locks are built in such a way that they will “recognize” one or more keys.
If we have your three keys, A, B, and C, and all of them are unique, we can design Lock A to recognize both Key A and Key C, and Lock B to recognize Key B and Key C. Thus neither of the locks will recognize the other’s first key, but they can _both_ recognize Key C.
The way this actually works is by manufacturing the lock to be able to be opened in two separate positons instead of just one. If we then happen to make the second position the same for all locks, we now have the ability to make a “master” key that will fit that second position in every lock.
ELI5 answer:
Each pointy edge on the key is made to push a little metal pin out of the way so the lock can turn.
Some locks may use different pins in different spots.
A lock with small pins in the front would need a key with small edges near the handle.
A lock with large pins in the back would need a key with large edges near the end.
A key with large edges near the end and small edges near the handle could open both locks.
(It’s actually more complex than this, but this is the idea simplified)
Locks have pins in them that when aligned properly, the lock can turn. In each slot, there’s a driver pin and a key pin. Each one will a different length, determining how the key has to be cut to open the lock. When the gaps between the pins are all aligned with each other and the edge of the part of the lock that turns, called the shear line. When all of that lines up, the lock can turn.
[Visual explanation](https://thumbs.gfycat.com/AcceptableAccomplishedAfricangoldencat-mobile.mp4)
If you want a master for those lock, in-between the driver and key pins (in at least one slot) you add what’s called a master wafer. This adds another break between the pins, meaning there’s a different combination distances to push the pins that also opens the lock. To have several different locks that all open to the same master, ideally you would have all the pins but one be the same, and then the last pin has a different sized master wafer in each lock such that the master key fits all of the locks.
For example I’ll use arbitrary numbers for pin lengths:
1, 2, 3, 4
1, 2, 3, 5
1, 2, 3, 6
Each one needs a unique key, but if we give each one a master wafer in the last spot of lengths 3, 2, 1 respectively
1, 2, 3, 4/7
1, 2, 3, 5/7
1, 2, 3, 6/7
Each one’s unique key still works, but a key for 1, 2, 3, 7 will fit all 3 locks
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