A mezuzah is parchment scroll, on which the Shema is handwritten by an expert scribe.
A mezuzah mounted on the right side of the doorpost designates the home as Jewish, reminding us of G‑d and our heritage. It is also a symbol of G‑d's watchful care over the home. The placing of a mezuzah on the doors of a home or office protects the inhabitants — whether they are inside or outside. (www.chabad.org/mezuzah)