Unfortunately, most people do not have their Mezuzot checked unless they face a situation of tragedy, Heaven forbid. But in truth, Halacha requires that Mezuzot be checked by a qualified Sofer (scribe) once every 3.5 years. Many people neglect this Halacha because they mistakenly view the Mezuza’s primary purpose as offering protection and serving as a kind of "charm" for the home. While the Mezuza certainly does offer protection, and we ought not belittle this function, the primary reason for placing a Mezuza on our doors is because the Torah obligates us to do so. As such, even in the absence of trouble or calamity, Mezuzot must be periodically checked to ensure that the residents in the home properly fulfill the Torah obligation of Mezuza.
After the Mezuzot are checked, one reaffixes them to the doorposts after reciting the regular Beracha ("…Asher Kideshanu Be’misvotav Ve’sivanu Li’kbo’a Mezuza"). Even though the Mezuzot were found to be valid, one nevertheless recites a new Beracha before reaffixing them, because when he removed them he did not know for certainty whether they were valid. As such, the replacement of the Mezuzot amounts to affixing them anew and thus warrants the recitation of a new Beracha. One recites a Beracha before affixing the first Mezuza, and this Beracha covers all the Mezuzot that he subsequently affixes.
Another common misconception regarding Mezuzot is that they are not required in rooms that the family does not use regularly as part of daily living. Many people mistakenly assume that they need to place a Mezuza only on the front door and in the bedrooms, living room, dining room and kitchen. In truth, however, Mezuzot are required in all rooms in the house that meet certain requirements of size and the like. This means that basements, boiler rooms and garages require Mezuzot just like the other, more frequently used rooms of the home.
Summary: Halacha requires having one’s Mezuzot checked by a competent Sofer (scribe) every 3.5 years. After they are checked, one reaffixes them with a Beracha. Mezuzot must be placed on all rooms in the home that meet the minimum size requirements, even rooms that are not used regularly as part of the daily living, such as basements, boiler rooms and garages.
