There is an opinion that it is forbidden to move a
mezuzah on Shabbos because it is מוקצה מחמת חסרון כיס (unmovable because of
its high value). Nevertheless, if a mezuzah falls from its case on Shabbos
and lies in a place which is inconsistent with the respect we should feel
for it, it is permitted to remove it and place it in safe-keeping.
Is it permitted to return the mezuzah to its place in a
way that does not involve hammering nails? The issue is discussed among the
poskim and there are opinions which allow a person to return a mezuzah to
its case if he doesn’t attach it.
When, on Shabbos, a person returns a mezuzah to its case
in a way that is permitted, he does not recite a blessing, even though,
during the week, we do, even when we return it to its case immediately,
because it is considered היסח הדעת. The reason is that on Shabbos it is
forbidden to put a mezuzah in place, so it is inappropriate to recite the
blessing on doing it. Even on Motzei Shabbos the blessing is not recited
because the poskim are in doubt as to whether or not the blessing can be
said after the mezuzah is affixed, and when in doubt, we do not recite
If the mezuzah falls from the front door, is a person
allowed to enter his house? Most poskim agree that he can. Since he is
withheld from affixing the mezuzah by the laws of Shabbos, he is not held
responsible for the fact that at that moment he is not fulfilling the
positive commandment of placing a mezuzah on the door post.
If the mezuzah fell during the week because the case was
not attached at the bottom, it should be attached when the mezuzah is
returned. If it is not well attached both above and below, it is considered
a hanging mezuzah, which is posul according to most Rishonim.