This isn’t really a gadget, but the technology on display is rather impressive, and it’s probably good to know about anyway, in case you make a lot of clandestine audio recordings. British scientists have determined a way to authenticate audio recordings (or prove they’ve been tampered with), by matching infinitesimal variations in the sound that correspond to variations in the power grid. They claim it’s the biggest advance in audio forensics since the analysis of the Watergate tapes.

The technology, called electrical network frequency analysis (ENF) was made possible largely by the move to digital recording in video and audio devices, which keeps perfect time — unlike analog devices, which suffer from microscopic changes in recording rate as the batteries get low, the device is jarred, or the tape reel runs out.

Digital recordings and their accurate timestamps allowed researchers to reliably detect in a given recording the tiny, tiny background noise created by the electrical grid; this pattern is then compared to a central pattern database, at which patterns from all over London are recorded and stored. If the patterns don’t match, or there are multiple patterns, it suggests tampering.

The slightly scary part: they’ve been making recordings of the grid patterns every one and a half seconds for the last five years. I mean, it’s not like they were covertly installing microphones in everyone’s bedrooms or anything, but it’s a little creepy to know that a sort of really grainy snapshot is being taken forty times a minute, wherever you are in the city.

via British forensic audio analysis tool has been passively monitoring London for five years.