I didn’t think I wanted to mention the inspiration for the hacking whistle here, since I liked the thought of readers thinking of it as a ridiculous cartoony thing like a portable hole, only to have that eureka moment some time later when they read about the real thing it references. But, the story behind it is too cool not to share. You’ll want to read about John Draper, Phreaking, and the 1971 Cap’n Crunch Bosun Whistle. For now, I’ll just point you here: wikipedia.org/wiki/John_Draper