I'm writing a open-source library (https://github.com/RaphaelJ/libhum/) and a webapp (https://datethis.app:8080/) that detects the Utility Grid noise emitted by electrical devices (A/C, motors, appliances ...) from Video/Audio recording.

It then tries to date the recording by matching it to historical data.

The signal processing part is getting decent. I'm still trying to collect more reference signals in RU, UK, China and Japan.

Tom Scott made a video about the idea: https://www.youtube.com/watch?v=e0elNU0iOMY