Bullet casings can be carved into emergency whistles
It is always a good idea to carry a signal whistle on when hiking or just out exploring nature. If buying one isn’t appealing, it’s possible to fashion one out of an old bullet casing. Just make sure that it is long and narrow.
First, shave the narrow tip of the bullet casing by rubbing it against a rock or cement. Then, grind a hole by putting the casing’s side perpendicular to a sharp-edged stone or slab. It should be flat at the top and have a sloping curb down the rest.