Doors with a twisted tab lock are still easy to get past even if that tab is set to "lock." These locks appear on the handle of a door, when either facing laterally or vertically the door will be locked or unlocked. The lock is set from inside the door. But unlocking the door even with the tab set to the lock position is doable with items that are typically found around the house.
Find a paper clip. Bend the paper clip so that a portion of it is long and straight enough to insert into a small hole on the door knob.
Locate the hole on the door knob. It should be located where the back top curve of the knob meets the piece of the handle connecting to the door.
Insert the paper clip into the hole. Move the paper clip around until it catches something or a click is heard. There is a small button inside the knob that serves as the locking mechanism. Without too much time or effort the paper clip should contact the button and release the lock.
Of course tools can also be used to take the door off its hinges or to remove the knob from the door, but using a paper clip or a similar piece of wire, like a coat hanger is easier and has less potential for damage to the door, the handle or the lock itself.