Amulet.
A small object, often worn, carried, or hung in a doorway, kept for its protective influence against harm or misfortune.
An amulet is an object kept for protection. The word descends through Latin amuletum, with roots that may go back to Arabic himalat, "something carried." The function is the older one in human history: to ward off harm, evil, illness, or bad luck. Where a talisman is traditionally said to attract, an amulet is traditionally said to repel.
Examples are everywhere. The Egyptian Eye of Horus, the Mediterranean nazar against the evil eye, the hamsa hand, Roman bullae worn by children, Norse rune stones, and small inscribed gems set into rings throughout the medieval world. Many of these were stones, often engraved with names, sigils, or short inscriptions and worn on the body or hung in entrances.
In modern crystal practice the amulet idea survives quietly. A piece of black tourmaline by the front door, a small obsidian in the car, a hematite ring worn in crowded places. The mechanism people describe is not so different from what the tradition has always claimed: an object that holds a clear protective intention reminds the carrier to stay grounded, alert, and willing to leave situations that do not feel right.