Examples from Kuwait, Iran, Oman, and Yemen. Some of the doors from Iran show the typical two knockers for men and women. They give different sounds. In a society where women live in seclusion (either at home or veiled), it seems to be vital to get to know who is knocking (and therefore who has to open the door).
More samples may be found in the beautiful book by Jehan and Tareq Rajab about The Carved Wooden Doors of Kuwait, the Gulf, and Yemen.