What is watch winder and what is it's purpose?

A watch winder is a device used to help automatic watches remain in good condition when they are not worn. When automatic watches are worn, the moving weight inside of them winds the wind through the force of gravity as the watch is moved on your hand. However, when the watch is not worn, the moving weight cannot move around to wind your watch and lubricate the internal devices. Therefore, the purpose the of the winder is to wind the watch and keep it in condition.