If you look at the start of that episode, there is another crazy thing in there, a device which allows you to "see" the bits on a credit card track. Apparently

If you look at the start of that episode, there is another crazy thing in there, a device which allows you to "see" the bits on a credit card track. Apparently something called "magnetic viewing film" can allow you to see the bits on the magnetic stripes of credit cards. I had never heard about this before. Link to video time: https://archive.org/details/bbc-connections-1978/Connections/S01/S01E08+-+Eat%2C+Drink+and+Be+Merry.mkv?start=176.1 https://archive.org/details/bbc-connections-1978/Connections...