When I was in Israel last week, I noticed that each hotel room door had a little box outside on the doorframe. I learned that it is called a "mezuzah."
They must always be on the door frame, not the door. Also they must also always be outside the door, not inside.
They must be situated at about shoulder level, so that they may be kissed or touched upon entry.
They are often leaning in towards the door, to signal that this is the direction in which God should pass.
Inside the Mezuzah case is a Kosher parchment, with two handwritten paragraphs of the Torra. The writing must be done by a licensed Sofer Stam, a scribe who can transcribe the Torah. There must be intension in the writing of it.
The verses say such things as there is only one God, you must teach your children about the God, you must love your children, and so on.
The effect is that when you go into a Jewish home, you are made aware of the laws written on the scroll.
Many people think that it is a good luck charm or a home protector. Some people even have special ones for their cars, etc. thinking it is an amulet against evil. It is none of these things - it is a reminder that helps one make conscious of their responsibilities to God.
I bought the Mezuzah pictured above. When I looked at my credit card statement, it was about four times more than I thought it was. I'm terrible with currency conversions. And I didn't know it was ceramic and also 24K gold. It is not just a tourist souvenir, but rather a special item one may give someone on a special occasion, and now I appreciate that.
I will fix mine in the right way on the outside my front door, and knowing me, I will probably also touch it each time I enter the house and it will make me happy.
However, I have decided not to get a scroll to go inside. People have a lot of different opinions about this, but to me, as I am not Jewish, it just doesn't feel right to have the scroll. The case is enough to give a nod to this interesting Jewish custom.