Back when I was doing z80 programming on my TI-83+, I would sometimes us an AM radio as a very crude debugger. Programs stuck in busy loops would generally have a very distinct sound, and you were often over time able to learn what other parts of your program sounded like too.
Yeah, my understanding is that doing that became difficult even on the higher end 83+/84+ series calculators as the clockrate went up, though I haven't actually put that to the test.
