Many people “grid” their homes with selenite and tourmaline, but I also keep a piece of tourmaline with a selenite wand near the front door of my home. The front door tends to get a lot of visitors and faces some energies that I am not interested in having in my home.
Both black tourmaline and selenite are wonderful crystals for purifying, cleansing and protecting your surroundings. In the case of putting both near your front door, black tourmaline protects and shields negative energies of unwanted people or negative energies entering your home and selenite purifies and cleanses the space around it. Selenite can also bring a sense of peace and tranquilly.
Some people do all doorways, and windows.
Here's a few sets made up.