This is not the site to discuss the laws of putting on tefillin or of putting up mezuzot on one’s house. But I would like to mention that according to Jewish mysticism, all the blessings for health, parnassa, children and even shalom bayit come down through the tefillin and mezuzot. And they bring protection in all matters in life. So it is of utmost importance for every boy from the age of bar mitzvah and on to put on tefillin every day (except Shabbat and yom tovim) . And it is of utmost importance to be sure all doors of one’s house have kosher mezuzot and that the mezuzot are checked each year to be sure they do not become “passul” (meaning none of the letters get faded, worn out, or rubbed off etc. rendering the mezuzah unkosher).
To affix a mezuza there are many laws as to the proper placement on the door way and which doors require mezuzot. For example, a door way that has a lintel and two proper door posts needs a mezuza.
So mezuzot and tefillin are so essential to a proper Jewish household and to protection. And it is not enough just to put a mezuza on the front door. Every doorway should have a mezuza.
And whenever one checks mezuzot to see if they are kosher properly or have been in any way affected by weather etc., one should also be sure to check if the placements of the mezuzot are correct. Every aspect of the mitzvah of mezuza can affect the family members living in that house.
There are so many stories of the Lubavitcher Rebbe instructing people to check their tefillin and mezuzot when they were ill or had any number of problems in their lives. In fact the lives of hundreds and thousands of Israeli soldiers were saved due to the tefillin campaign the Lubavitcher Rebbe initiated during the war. This brought protection and salvation to the soldiers.
The tefillin protect the mind and the heart.
Mezuzot protect all members of one’s household when they are in the house or out of the house.
But it is important to be sure one buys mezuzot and tefillin from a reliable sofer (scribe) or reliable organization to make sure they are truly kosher and of top quality (mehudar). It is also advisable to have new tefillin and mezuzot checked before being used because sometimes there are problems from the time of writing the letters and one should not assume if something is new it is perfect. Always check!