Q. I have mezuzos that were checked properly when bought and they are stored in transparent glass tubing containers where you can clearly see that even the plastic they are wrapped in, is sealed and intact. Do you have to check them every three and a half years?

A. Tosafos (Menochos 43a) mentions that the reason for checking out the mezuzos twice in a shemita cycle is not for the purpose of verifying that it was well written and there are no mistakes or misspellings, but rather to confirm that it has not been damaged (by humidity or heat) and it is still complete.
Therefore, Chasam Sofer (283) rules that no professional sofer is required and anyone can check it to ascertain that the mezuzah is still there, there is no water or rot damage and no ink has been erased from any of the letters.
Horav Shlomo Miller’s Shlit’a opinion is that in need you can rely on the fact that you can see no damage to the outside parchment of the mezuzah and the letters of Hashem’s (Shakai) name are complete. This applies only when the mezuzah is in the interior of a year-round climate controlled house and also not exposed to the direct rays of the sun or damaging humidity.

Rabbi A. Bartfeld as revised by Horav Shlomo Miller Shlit’a