A mortise lock is designed quite differently than a cylindrical or tubular lock. A mortise lock is a box-like unit that is installed in a mortise in the edge of the door. The interior and exterior trim as well as a mortise cylinder are installed through holes drilled from the face of the door to the mortise opening. Mortise locks used to be the standard for residential locks, but were largely replaced by cylindrical and tubular design locks. Modern mortise locks are still common in commercial buildings. They are less common in residential settings largely because modern mortise locks are considerably more expensive than cylindrical and tubular locks.