Some people are using this type of lock for a back or side door and usually leave the key in the lock on the inside while using one of the other doors. In these older doors there is usually a large crack at the bottom that may allow access to open it. After determining there is no easy way in and that the building is securely locked you can use this very old and simple trick that is often effective on older kinds of buildings. It is require using the bit key lock which piece of molding that easily can be removed. You start by slipping a piece of thin, stuff paper under the door. Then with another key or pick, jiggle the key that is set on the other side of the door until you can make it fall out off of it. When the key falls out it will most likely land on the paper. Carefully pull the paper out and the key will slide under the door.
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