A brass belt buckle with a simple setting supporting a tourmaline. This gemstone can be depressed
twice a day, whereupon the wearer is surrounded by an invisible barrier. Within the barrier the temperature, air quality and purity, pressure, etc are maintained - environmental conditions inimical to continuance of life do not pass. The barrier makes the wearer immune to airborne poisons and diseases, improves the wearer's armor class by 1, does not interfere with the manipulation of objects and will persist for up to 4 hours.
taking inspiration where you can get it
8 hours ago