Many believe the mezuzah is good luck and offers protection to those who live in a house with a mezuzah. This dates back to the 10 plagues when G-d passed over all the houses with symbolic mezuzot in the killing of the first born. According to 13th century scholars, no demon has power over a house with a mezuzah. If a family has suffered bad luck or misfortune it is customary to check the mezuzah to make sure the klaf is still kosher and if you replace it you can change the energy in the house.