This Instructable shows you how to transform a common ballpoint pen into a survival whistle which will fit inside an Altoids tin and still work as a pen. This multi-functionality helps to save space in the tight confines of the tin.
DISCLAIMER: Though this whistle is ear-splittingly loud when configured properly, I have not tested it in a survival situation. Please use your own judgment on whether your end product is good enough for a real survival situation, if that is its intended use. If it isn't good enough for that, please consider shelling out the money for a factory-made whistle.
--small piece of sandpaper
--Papermate Eagle ballpoint pen
--it is quite possible there are other pens which will also work; I have selected this one for several qualities. First, there is no hole in the barrel of the pen--for some reason many ballpoint pens have a tiny round hole somewhere on it. Second, the ink cartridge is easily removed with your fingers. Third, the end piece is a separate piece that can pop out.