This client called our mobile locksmith service because her key had stopped working in her front door and she didn't have a key for the sliding glass door in the back. One of our technicians inspected the troublesome lock and saw that the key would go in and turn the lock cylinder, but it wouldn't disengage the lock.
After our technician successfully unlocked her front door, we went to figure out what was causing the problem. It only took a few minutes to figure out what the problem was. The part in her lock that kept the tailpiece attached to the lock cylinder had broken off from wear and tear. Even though the key was working and it turned the lock cylinder, the tailpiece wasn't connected and wasn't pulling on the latch to open the door. The tech replaced the broken tailpiece connector and restored the lock to working condition.
The client then asked us to make a key for the sliding door in the rear of the house that she never had the key to incase the same problem occurred again and she got locked out. Our tech re-keyed the sliding door lock to match the front door lock. Now she only needs one key for the front and the back doors. In most cases its more viable to have one key work for all the locks in your home. This is because if one of the locks stops working, you only need one key to open up any side or back doors you may have, avoiding a lock-out situation.