Alam Turing used the "hoot" instruction on the Manchester computer in the 1940s to signal different things for debugging https://www.bbc.com/news/magazine-37507

Alam Turing used the "hoot" instruction on the Manchester computer in the 1940s to signal different things for debugging https://www.bbc.com/news/magazine-37507707 https://www.bbc.com/news/magazine-37507707