Last edited 11 Mar 2021

How door locks work

This iron metalwork object is a 16th century rim lock and key from France.

1 Introduction
2 Rim locks
3 Cylinder locks
4 Related articles on Designing Buildings Wiki

[edit] Introduction

A door lock is a mechanism used for security purposes - preventing a door from being opened by unauthorised people. There are many different types of door locks. Two of the most basic types of locks are rim locks and cylinder locks.

[edit] Rim locks

One of the oldest types of locks, the rim lock uses a bolt and key to secure the door. The bolt in the lock is moved when the correct key is inserted into the mechanism and turned. This action presses the tumbler - which is kept in place by a spring - up, and frees the bolt.

Next, the key bit engages with the corresponding notch under the bolt. Turning the key moves the bolt until the catch of the tumbler fits into next notch on the top of the bolt.

In simple locks, this completes the locking action. Greater safety is provided by a lock having not one, but several tumblers.

[edit] Cylinder locks

A cylinder lock uses a rotating mounted plug. When locked, the cylinder is held in place by several pin tumblers that have been moved into the proper position by springs. This allows the pins to fit into corresponding holes in the cylinder and keep the cylinder from moving.

A key is then inserted into the lock, which raises the pins so their tops move to a position that corresponds to the top of the outer surface of the cylinder. When the different segments of the tumbler are not connected, the cylinder can move freely when the key is turned. This allows the bolt to move and unlocks the door.

Another type of cylinder lock is the disc tumbler lock. This type of lock uses movable discs instead of pins to lock the cylinder.