There are three main types of door locks: the bunt-bit lock is a door lock of simple design. The security results solely from the shape of the keyhole, which prevents the insertion of a differently shaped key bit. Since these locks can be opened easily without a suitable key, they are only suitable for interior doors with increased security requirements. The bathroom/WC lock is a special variant of an interior door lock is equipped with a rotary knob on the inside and with an emergency opening from the outside. The profile cylinder lock is the standard lock for front and apartment doors and provides a higher level of burglary protection. Inside a profile cylinder, there are spring-loaded, split pins that block the cylinder core. This can only be turned when a key with a matching profile is inserted.