How Does a Rim Deadbolt Lock Work?

What is a Rim Deadbolt Lock?

Rim deadbolt locks are most frequently seen on residential front and back doors. When the lock engages, a bolt extends out from the side of the door and nestles into a notch in the frame. This prevents the door from moving. To extend or retract the bolt, a key is used to rotate a cylinder lock. When the bolt is retracted, the door can swing freely again. The cylinder lock is the "key" to the deadbolt lock.

Rim deadbolts use a cylinder lock. This kind of lock works by using a key to turn a cylinder, which turns a cam, which turns a plug, which then either slides the bolt forward or pulls it backwards. Other locks work in much the same way, except that they use a spring system to "release" the lock. In deadbolt locks, whether the bolt goes forward or slides backwards depends on which way the key is rotated. All deadbolt locks are considered very secure, as the bolt is quite heavy and it is hard, if not impossible, to slide it back into the door without a key. For this reason, it is recommended by home security experts that all residential front doors feature some type of deadbolt lock.

The cylinder lock cannot be rotated without the proper key. Within the cylinder is a pin-and-tumbler set-up. These tiny pins are of varying height and are grouped in pairs. Each pair sits in a tube, or shaft, which runs through the cylinder and into the surrounding area around the plug. Tiny springs sit at the top of each shaft, which keep the pairs of pins in place. When there is no key in the lock, the bottom pin in each pair sits completely inside the plug. The upper pin sits halfway inside the plug, with the other half extending into the housing.
Once a key is inserted into the lock, the "notches" in the key serve to push the pins up to different heights. Any key that does not have the correct notch pattern will push the pins in such a way that they are all still partly in the plug and housing. This prevents the cylinder from rotating. The right key, however, will push the pins to the correct height, which is at the shear line. The shear line is the point where the cylinder and the housing meet. The upper pins will be all the way in the housing, and the lower pins will be all the way down into the plug. This will allow the cylinder to rotate.