The people opposite my house nailed a nail on the door. What does that mean?

There are two explanations for hanging nails, both of which are influenced by the superstitious thoughts of the elderly.

The first is to hang a mirror to shine/ward off evil spirits.

The second type is rooting or nailing, usually in a row of three or five, to keep money or nail monsters that have entered the house and deter foreign monsters.

Out of my understanding of pre-liberation thoughts, people across the street did this, and my family must do the same. . .