Mezuzah

A mezuzah is a box with a scroll in it. Jews put on mezuzahs their doors. The mezuzah is written by a Jewish scribe called a Sofer.
Most people put their mezuzah on the front doorpost, but halakha requires that every room with 36 square feet (but not bathrooms) should have a mezuzah on the right side of the doorpost.
There are 4 different types of writing styles for Mezuzahs: Beis Yosef, Arizal, Sephardi and Alter Rebbe.
In the United States, prices for Mezuzahs range from US$50 for a cheap mezuzah, $85 for a medium quality, and $130-150 for a high-quality mezuzah.
The idea for mezuzah comes from Deuteronomy, chapter 6: "And you shall inscribe them on the doorposts (mezuzot) of your house and on your gates."