An electric strike is an access control device used for doors. It replaces the fixed strike faceplate often used with a latchbar (also known as a keeper) After the door is opened past the keeper, the keeper returns to its standard position and re-locks when power is removed or applied, depending upon the strike's configuration. Locking devices can be either "fail safe" or "fail secure". A fail-secure locking device remains locked when power is lost. Fail-safe locking devices are unlocked when de-energized.