Hackaday did a breakdown of the methods and how they worked, and one of the more modern methods was optical comparison to a live broadcast https://hackaday.com/

Hackaday did a breakdown of the methods and how they worked, and one of the more modern methods was optical comparison to a live broadcast https://hackaday.com/2021/01/18/tv-detector-vans-once-prowled-the-streets-of-england/ https://hackaday.com/2021/01/18/tv-detector-vans-once-prowle...