All of the components of a lock work together so that they only open with the right key. The idea is that one key opens one lock, but not another. In Dallas, even if you and your neighbor have the average Kwikset deadbolt, you will not have keys that open each other’s locks (or that is the hope anyway).
This is because of how the key works. You insert the proper key for a lock into the keyhole. The grooves raise the key pins (which are different sizes) on the key. Both the key grooves and the key pins correspond so that even with the pin stacks having different sizes, they are all elevated to the shear line.
When the wrong key is inserted, a low cut on a key might not elevate the pin stack high enough for the driver pin to clear the shear line. A key groove that is too high might elevate the pin stack so that the key pin is moved to block the shear line.
Once the pins are on their respective sides of the shear line, there is a gap that allows the plug to turn. You can then turn the key, and the plug will rotate. The rotation of the plug moves a cam or tailpiece that retracts a bolt or locking pawl. The lock is then open.
Lock picking works a little like a key in slow motion, and with the sequence of events jumbled up. For example, you start by adding a bit of turning pressure to the plug. This puts tension on the pin stacks, which you will feel released as the lock is picked.
You need to move each pin stack so that the driver pin gets stuck on the bible side of the shear line. This is the slow-motion part of the lock picking process. Where one insert of the proper key would align the pin stacks, now you need several inserts and some deft movement of the lock pick.
You must understand that lock picking works by tensioning and manipulating the pin stacks, similar to how a key would open the door. This is the essential premise of lock picking.
Lock chambers have to be milled into the metal and rarely end up in a perfectly straight line or with the exact diameter as each other. This means that some of the chambers lean more toward the right or left.
When you apply rotational tension to the plug, you can find the binding order of the pin stacks, by feeling for resistance. That resistance is the pin stack grinding against the metal of the pin chamber, meaning it is ready to set.
The springy pin stacks do not have resistance because their pin chambers align farther off from the direction of rotational pressure. And once the binding pin is moved above the shear line, that pin chamber’s less than perfect alignment allows the plug to turn a bit.
As the plug turns, the driver pin is given a ledge to rest on, so that the spring tension will not send it back into the plug.