This is a simple keychain whistle. I really like itTohmisThe whistle is a redesign of https://www.thingiverse.com/thing:3130078, but I found the high-pitched whistle a bit harsh on my ears. So, inspired by that, I redesigned it to be one-sided and extended the resonance tube, so it now sounds more like a train whistle and is more comfortable for my ears. The volume of this whistle isn't as loud as the original one, but it's an interesting little project.