A knocker, handle or caller is an articulated piece of metal located on the exterior doors of houses that serves to call its occupants by knocking on the door.

The first knockers in the Middle Ages consisted of little hammers suspended from the door leaves on the outside. The most typical and oldest form is that of a ring or hoop, made of iron in the oldest ones, generally attached to a bronze head. They were hit on a rather fat nail head. These knockers also served as handles and on the doors of some churches they were a sign of asylum "Asylum (refuge)") that was required by holding onto said ring.

Saint Gregory of Tours speaks of such an ancient custom. Said head was that of a lion or a griffin or a chimera "Chimera (mythology)"). Of lions were, for example, those of the knockers on the door of the cathedral of Puy-en-Vélay") of the century and another of the century of the western door of the cathedral of Noyón"). This type of knockers were especially assigned to the doors of churches, undoubtedly because the tradition of the right of asylum requested it.

The hammer shape was used more in private homes. The oldest ones were very simple and were decorated with burin engravings. From the 19th century, there are many examples of wrought iron, among which there are beautiful ones, delicately forged and chiseled, and with a heraldic shield painted in the corresponding colors. As time went by, these knockers fell somewhat into disuse and were only preserved for the doors of rural rooms. It is known that on the doors of the castles there were knockers, undoubtedly attached only to the leaves of the posterns without a drawbridge or to the doors of the external walls.

In Spain there are still many doors of churches and stately homes with very notable examples of knockers and knockers, many of them of artistic value. The oldest and also most common form was that of a ring suspended either from a ring or from a lion or griffin head that stands out in the center of a circular plate or at the vertex of a cone whose base is above the door. The ring is usually faceted with four faces decorated with engraved linear work that is generally repeated on the disc. An influence of Arab art is discovered in all the characters of these knockers.

In the cathedral of Bayonne, France, there is a very notable example in iron, of very rich Spanish work, with an ornament in the shape of a griffin's head and holding the ring with its mouth. It is estimated that it dates back to the 14th century and, without a doubt, this artistic type persisted in the 14th century since there are many specimens on the peninsula that only differ in size. In many of them, such as the Mudejar door (1st century) of the Chalices sacristy in the cathedral of Seville, the head of the griffin stands out from the center of a star.