Interior Door Locked From Inside
For a push-button lock, you will need to take a small screw driver of a wire paperclip and open it. Alternatively, you could use a wire clothes hanger as well. Take the wire and insert it into the hole located in the center of the doorknob. Then, push the tip of the paperclip or clothes hanger straight into the hole and try to keep it as straight as possible. If you keep it straight, you should feel the lock on the other side of the door. Apply pressure until the lock pops and you are able to turn the doorknob.
For a twist button lock, insert a flathead screwdriver (Don’t have a screwdriver, see below) into the slot located on the outer knob. Again, you will need to insert the screwdriver as straight as possible. Once it’s fully in, turn the screwdriver slowly clockwise. You will need to turn the screwdriver about a quarter of the way, in order to open the door. If the screwdriver turns more than that and the door still does not open, your screwdriver probably did not fit into the internal slot designed to open the door, so you may need to try again or get a screwdriver of a different size. Scroll to the bottom of the page for a YouTube video.
A popular hiding place for an emergency key is on the top of door jambs.