How Do Locks And Padlocks Work? - Explain That Stuff

Locks and keys

by Chris Woodford. Last updated: August 7, 2023.

Dangerous criminals, gold bars, glittering jewels—what do they have in common? All are kept secure by locks and keys. Would the world be a happier place if no-one had invented such things? It just might be!

Imagine it for a moment. Anyone could steal anything, so perhaps no-one would bother owning very much or wanting anything more. No-one would live in a fancy house with valuable belongings, swan around in a luxury car, or earn more money than they could carry in their pocket. Perhaps that would be a better world, but it's not the one we live in! In our materialist modern age, we buy stuff, earn money, and buy even more stuff. We are what we own—and the only thing standing between a lifetime of slowly accumulated, valuable possessions and instant poverty is the lock on the door. Locks, then, are pretty important things, but have you ever stopped to wonder how they work? Let's take a closer look!

Photo: Most door locks have rotating cylinders and pins that slide in and out holding them securely in place until you insert the right key. Here you can see the cylinder removed from a door lock and the pins ready to pop out when the key is turned. Photo by Nicholas Alder courtesy of US Air Force and DVIDS.

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Contents

1. What is a lock?
2. How do locks work?
3. How a mortise lock works
4. Types of locks
5. How Yale locks work
6. Who invented locks?
7. Find out more

What is a lock?

In the very broadest sense of the word, a lock is a device that keeps valuables safe or restricts access to something that needs protecting. A lock can hold things out (protecting homes from intruders and banks from thieves) or keep them in (holding criminals in jail or animals in zoos).

Photo: A lock isn't simply something that's opened by a key: it's a piece of compact mechanical engineering that converts the rotary (turning) motion of your hand into reciprocal (back-and-forth) motion of the bolt that locks or opens something like a door.

Before the modern electronic age, locks were entirely mechanical and based on intricate mechanisms made from levers, wheels, gears, and cams. During the mid-20th century, locks became more sophisticated and automated and started to incorporate electrical and electronic mechanisms. But now information is valuable too and most of it is held inside hundreds of millions of computers that are all linked together through the Internet. Modern locks that protect computers are based on encryption—a way of securing information using complex mathematical processes.

How do locks work?

Most mechanical locks are fitted to things like doors and cupboards and have two physically separate parts. One part is fitted to the frame (the static part of the door) and is essentially a sturdy, metal reinforcement for a hole cut into the door itself (to prevent the locked door from being opened with brute force). The other part of the lock fits into a rectangular hole in the door (known as a mortise) and consists of a metal mechanism that moves a heavy bolt into or out from the reinforced hole. The bolt slides from side to side when you turn a key clockwise or anticlockwise, so it has to be operated by a mechanism that can convert rotary motion (the turning key) into reciprocating motion (the sliding bolt)—something like a cam or crank. If that were all that a lock consisted of, every key would be able to open every lock. So the other essential part of a lock's mechanism is a set of fixed or moving metal pieces (wards or tumblers) that engage with slots cut into the key, ensuring only one key can rotate, turn the cam, slide the bolt, and open the door.