I guess I don't get it. I understand the concept of improvisation, it's fundamental to survival skills. You can't possibly carry everything with you. It's also fun to do and they tend to be good skills to learn, even if you normally already carry better gear. I also understand improvising a solution to an expensive piece of gear you can't possibly afford. However, I don't understand this sort of thing. A very good and effective whistle that requires no skill whatsoever to use, you can be near death and still make lots of noise, can be had for a very few bucks, pennies in some cases, will take up not much more space in your pocket, perhaps less, than that cartridge and is available easily from innumerable vendors. Why improvise something not nearly as effective when you can afford to carry the best and your life might have to depend upon it?