Is it permissible to put a Mezuzah on a chain and wear it? Some people want to wear a Mezuzah for protection like an amulet, or to protect from Ayin Hara (evil eye.) Is this permissible?
Chacham Ovadia Yoseph asks this question in Halichot Olam, Helek 8, page 216, and Rav Moshe Feinstein also asked this question in Igrot Moshe, Y"D, Helek Bet, Siman 141. They both came out saying that it is permissible to put a Mezuzah on a chain and wear it. Of course it should be contained within a case. Again, they rule it is permissible.
The question was also asked if you can put a Mezuzah in your car. There are some people who put a Mezuzah hanging from the mirror in their car. According to the Halacha, it is NOT proper to hang a Mezuzah in a car. However, it is permissible and OK if you want to put a Mezuzah on a dashboard laying flat. There is a difference between hanging a Mezuzah on your body and hanging one on a car mirror or something like that. The Gemara talks about the sin of hanging Tefllin, Chas VeShalom, on a wall. Hanging Tefilin on a body would be different though as the practice of a King was accepted when he used to walk around with a Sefer Torah on his arm like an amulet. So wearing a Mezuzah for protection is permissible but hanging a Mezuzah in the car is not permissible. Chacham Ovadia Yoseph is lenient though on putting a Mezuzah in a car as long as you put it flat on the dash board, or glove compartment, but not dangling from the mirror.