By Msgr Stephen Rossetti at catholicexorcism.org:
A possessed woman was away from her room on an errand. Not known to her, I blessed and exorcized it using holy water. I also sprinkled exorcized salt in the corners on the floor. Then I took exorcized oil and made a sign of the cross on the door, windows, and lintels. But when I left, nothing different could be seen by the human eye.
The next day, she texted me:
Possessed Woman: Did you do something to my room?
Priest-exorcist: Why do you ask?
Possessed Woman: You blessed my room.
Priest-exorcist: How could you tell?
Possessed Woman: Something changed. They [the demons] hated it They still do.
This brief exchange was illuminative. First, it helped confirm the woman was possessed. She had “occult knowledge.” There is no way she could have known I blessed and exorcized her room. She received this knowledge through the demons. Having occult knowledge is a strong sign of true possession. Second, it confirms the power and importance of having a priestly blessing, especially blessing our homes. The demons hate it and are repulsed by it.
Another possessed woman said that when she goes near a blessed home, she has great difficulty entering it, much like a church. A third said when she entered a blessed house, she could see the demon, that typically tormented her, stay outside. It peered through the window while she was inside but did not enter. A blessed home is a holy place and the demons in the possessed are repulsed by anything holy.
All should have their homes blessed, preferably by a priest who “should gladly cooperate.” But if a priest or deacon is not available, the Church’s revised Book of Blessing (1989, pp. 237-242) allows a home to be blessed by a layperson. After an Introduction, Readings from Scripture, and Intercessions, the lay minister, with hands joined, prays the Prayer of Blessing:
“Lord, be close to your servants who move into this home (today) and ask
for your blessing. Be their shelter when they are at home, their companion
when they are away, and their welcome guest when they return. And at last
receive them into the dwelling place you have prepared for them in your
Father’s house, where you live for ever and ever. Amen.“
Then the people and the home are sprinkled with holy water while the minister says: “Let this water call to mind our baptism into Christ, who has redeemed us by his death and resurrection.“