You probably have what is called a Schlage F series entry lock. One of the 'features' of a Schlage F series lockset is the interior knob is always unlocked to allow free egress at all times. I am assuming this is your issue... does the lock button on the inside turn or does it turn and push in? If the button only turns it is a F Series.... if it turns and pushes in it is an A series Schlage. If the screws are visible on the inside of the lockset rose it is an F series... as the A series locks have concealed screws.

If you have an F series Schlage you are better off replacing it for a number of reasons. First being security. These locks are sold under the Grade 2 UL designation (meaning light duty commercial duty) ... but are likely one of the least durable grade 2 locks manufactured. These locks tend to yield quickly to a forced entry attack. I could gain entry into your home secured with this lock in under 5 seconds... no kidding.

Secondly, I have seen numerous F series locks malfunction over the years.. never giving any indication of problems until the befuddled home owners were forced to contact me (a locksmith) to help them gain entry. The primary issue appears to be the deadlatch. (the springy part that protrudes from the edge of the door) With use the deadlatch will sometimes break and prevent the door from being opened despite the fact the lock itself is unlocked. Schlage now offers a lifetime replacement warrenty on F series locks. Not that it will do you much good when you are stuck outside of your home at night.

Lastly, of all residential lockouts I have done over 10 years of working fulltime as a locksmith, approximately 70% of the homes had Schlage F series locks. It would appear you are not the only one having issues with getting locked out.

Hope this helps!

G. Dunn