The Most Common Mezuzah Prayer

When affixing a mezuzah, the blessing is:

Hebrew:
בָּרוּךְ אַתָּה יְיָ אֱלֹהֵינוּ מֶלֶךְ הָעוֹלָם, אֲשֶׁר קִדְּשָׁנוּ בְּמִצְוֹתָיו וְצִוָּנוּ לִקְבּוֹעַ מְזוּזָה.

Transliteration:
Baruch Atah Adonai Eloheinu Melech ha-Olam, asher kid'shanu b'mitzvotav v'tzivanu likboa mezuzah.

English:
"Blessed are You, Lord our God, King of the universe, who has sanctified us with His commandments and commanded us to affix a mezuzah."

Psalm 121: A Traditional Prayer of Protection

Many people associate the mezuzah and "Shomer Daltot Yisrael" with these words:

Hebrew:
הִנֵּה לֹא־יָנוּם וְלֹא יִישָׁן שׁוֹמֵר יִשְׂרָאֵל

Transliteration:
Hinei lo yanum v'lo yishan, Shomer Yisrael.

English:
"Behold, the Guardian of Israel neither slumbers nor sleeps."

This comes from Book of Psalms and expresses God's continual watchfulness over His people.

A Traditional Home Blessing

While not a formal liturgical prayer, many Jewish homes display or recite:

Hebrew:
יְבָרֶךְ יְיָ אֶת הַבַּיִת הַזֶּה וְאֶת כָּל יוֹשְׁבָיו

Transliteration:
Yevarech Adonai et habayit hazeh v'et kol yoshvav.

English:
"May the Lord bless this house and all who dwell within it."

A Devotional Prayer Inspired by "Shomer Daltot Yisrael"

Although not a traditional text, one might pray:

Master of the Universe,
You are Shomer Daltot Yisrael, the Guardian of the Doors of Israel.
Watch over this home and all who enter it.
Let peace dwell within these walls, kindness fill these rooms, and Your presence rest upon this household.
Protect us when we come and when we go, and guide us in Your ways.
Amen.

This prayer captures the spiritual meaning behind the title "Shomer Daltot Yisrael" even though it is not part of the classical Jewish prayer book.