My sister begged me to get this for her. I ordered another that was defective and would not open, no matter what. She returned it. I replaced it with this. Excellent. They opened with no problem and everybody is happy. WHY, or a lock? Well, my nephew, my sister's son, keeps locking himself out of the house. he walks the dog and forgot his keys; he goes to school, and forgets his keys; he goes to football practice, and forgets his keys, then someone has to leave work to let him in. With this, he will always have a spare key, or now, until he forgets to put the spare key back, but we will cross that bridge when we get there.