The electrical hum that helps to fight crime (2012)

Another brilliant application of the ever-impressive FFT algorithm.

Makes me wonder though, I can't imagine it would be too hard for a tech-savvy threat actor to strip any existing AC hum from a recording, and then apply the hum frequencies corresponding to their date/time of interest. If this frequency database is used to perform verifications that can make life/death differences in a court of law, I assume it is secured and kept private. But then again, a truly dedicated rogue could maintain their own database, as the same hum is available to everyone...