Locked out of your house but have the key?

This sort of thing happens more often than you would think. I have attended 6 lockouts this month and 5 of these customers were locked out for the same reason – a set of keys was still in the lock on the inside. In each case the homeowner was understandably a little frustrated that they had a key in their hand but they couldn’t let themselves back in to the house.

The answer to this question lies in the mechanics of a pin tumbler lock and a euro cylinder.

Euro cylinder parts

To open a lock which relies on a pin tumbler design, the central core of the lock is turned. This has the effect of turning a tail or cam located behind the core, which in turn acts on some other part of the locking mechanism. Where the central core of the lock meets the body of the lock is termed the shear line. A basic pin tumbler lock has two sets of pins – top (driver) pins and bottom pins. The bottom pins are pushed into place by small springs held in a number of chambers. The bottom pins in turn push on the top pins. The pins are different lengths and block the central core from turning as they cross the shear line. To turn the central core the point at which the top pin meets the bottom pin must align to the shear line. The correct key for the lock will cause all the pins to line up correctly and allow the core to be turned. So far so good.

Lock shear line

UPVC doors typically have multipoint locks, which usually use euro cylinders as part of the design.

A double euro cylinder has a keyway on both sides (inside and outside of the door) and a cam in the middle to act on the multipoint lock gear box. Within the cam is usually a small clutch drive. When the correct key is put into one side of the lock, the tip of the key nudges the clutch drive into position, so that when the key is turned the cam is operated and the lock is opened. If a key is already in one side of the cylinder and turned even a fraction off of the entry axis the key is trapped by the top pins and the tip of the key blade is acting on the clutch drive. This means that from the outside a key cannot be fully inserted and cannot turn the outside core or act on the clutch drive. Even if the key were reduced in length the active side of the clutch drive is still engaged by the inside key and so the external key would not act on the cam.

If this is the situation you are in – please call 07767477879 and we’ll be with you as soon as we can. We always prefer non-destructive entry techniques getting you back in without damaging your door or lock day or night wherever you are in Essex.