These portable shrines are called »Gau«. They are encountered only in Tibet and in neighbored Buddhist areas. Nothing quite like them are is known in any other Buddhist country. It is not known how old the custom is in Tibet. Most known examples are generally dated to the last two or three centuries, although some maybe earlier.
The Gaus made of copper and brass were used to protect the owners from evil in everyday life, especially, when traveling.
They were filled with rolled prayers and blessed or sacred objects [seeds, small statues, Tsa Tsas or Tsaglis = small thangkas]. They were worn on a belt or sash over the shoulder or around the waist.
However, there are also larger Gaus that are not worn on the body. One finds them on house altars.