The mezuzah is the mitzvah mentioned in the Shema Yisroel, the special prayer Jewish people say twice daily. There are many laws describing exactly what a kosher mezuzah should be. A kosher mezuzah must be written by a learned scribe on parchment, just like a Torah scroll and tefillin. Many other detailed laws make the mezuzah kosher.
According to Jewish law, a mezuzah must be checked twice in seven years. However, many have the custom to have the mezuzah checked yearly, preferably during the month of Elul prior to Rosh Hashanah. A professional scribe checks the mezuzah to make sure that all its letters are intact. If even one letter gets erased or besmirched, the mezuzah needs to be repaired or replaced. A competent scribe can advise one what to do.
One place to have your mezuzot checked or to purchase new mezuzot is Chabad House Center. For more information, call or text Blumah Wineberg at 913-940-1113 or the Chabad House at 913-649-4852.