While playing with my Flipper Zero, I realised that the IR radiation that it reads does not have to be emitted by another electronic device! It can be a random analog IR 'signal' from a flame! Since Flipper can record raw IR data without interpreting it, there you go, a True Random Number Generator (TRNG)! I wrote a script that automates data collection and processing, here's a github link. It outputs your freshly generated true random number sequence into a file.

Robert Elder, the "my favourite Linux command" man, shows some cool micro-measurement equiplment , seemingly from the mid 1980s.