Amulet boxes or Ga'u made of copper and brass were used to protect the wearers from evil in everyday life. Especially, when traveling. They were with rolled prayers and blessed or sacred objects [small statues, Tsa Tsas or Tsaglis = small thangkas]. They were worn on a belt or sash over the shoulder or around the waist while traveling.
However, there are also larger Gaus that are not worn on the body. One finds them on house altars.