How to Open a Bedroom Door Lock
Bedroom door privacy locks usually have one of two locking systems: You either push in the button in the middle of the inside knob -- sometimes turning it while you push -- or you push and turn the entire knob. Either way, it's all to easy to do this before you close the door, only to find the door locked and you on the outside. All you need is a paper clip or a plastic card the size of a credit card to get back in.
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The Paper Clip Method
Most interior privacy locksets have a hole in the center of the outside knob. Straighten out a paper clip and push it into this hole to unlock the knob. If the lockset has a lever instead of a knob, the lock may be located next to the lever and, if so, the hole on the
other side of the door is opposite the lock. If you don't have a paper clip, you can use a length of 12-gauge electrical wire, a finish nail or a bobby pin.
The Credit Card Method
Your lockset may not have a hole on the outside knob. Don't panic -- you can open the door with a plastic card. A credit card is ideal, but if you don't want to scratch the magnetic stripe and make it impossible to get money from an ATM, any plastic-laminated card, such as a library card, will work.
Step 1: Slip the card between the door and the jamb.
If the jamb has a stop that prevents you from doing this, use a pry bar or hammer to pry it up far enough to slip the card behind it. You may have to patch some paint after you open the door.Source: ehow.com