8-bit home computers often (unintentionally) output noise over the audio output while the processor was busy. You could gain even more insight by putting an AM

8-bit home computers often (unintentionally) output noise over the audio output while the processor was busy. You could gain even more insight by putting an AM radio next to them. With practice you could get a rough idea of which part of your program the computer was in. Of course, we're talking about processor speeds <10MHz, you couldn't do this today, but maybe the same principle applies.