Door-posts

The Jews were commanded to write the divine name on the posts (mezuzoth’) of their doors (Deut 6:9). The Jews, misunderstanding this injunction, adopted the custom of writing on a slip of parchment these verses (Deut 6:4–9, and Deut 11:13–21), which they enclosed in a reed or cylinder and fixed on the right-hand door-post of every room in the house.

From Easton’s Bible Dictionary (1897), by Matthew George Easton.