The mezuza is put up on the right-hand side of the entrance to a home or room, on the top third of the doorpost. Some people position it upright, and some diagonally with the upper part facing inward. Before putting up the mezuza, a blessing is recited: “Blessed are You, Lord our God, King of the universe, Who sanctified us with His mitzvot and commanded us to affix a mezuza.” Women and men are equally obligated in this mitzva. A person should not sleep in a room without a mezuza even for one night.
The mitzva of mezuza applies both to the entrance of the home and to the entrance of each of the rooms within the home, except for the bathroom, because it cannot be used for holy purposes. A room is also exempt if it is tiny (less than 4 square amot, which is about 1.8 square meters or 19 square feet), since it is too small to be lived in. As for stores and offices, even though they are not lived in, they require a mezuza since people use them to store merchandise and equipment, and sometimes to eat in.
