This is somewhat analogous to smart meter technology that can infer what devices you have in your home simply by reading their electric consumption signatures. Unquestionably, the Intelligence community is already using this technology to identify people everywhere.

 New research into web-tracking techniques has found some websites using audio fingerprinting for identifying and monitoring web users.

During a scan of one million websites, researchers at Princeton University have found that a number of them use the AudioContext API to identify an audio signal that reveals a unique browser and device combination.

"Audio signals processed on different machines or browsers may have slight differences due to hardware or software differences between the machines, while the same combination of machine and browser will produce the same output," the researchers explain.

The method doesn't require access to a device's microphone, but rather relies on the way a signal is processed. The researchers, Arvind Narayanan and Steven Englehardt,

have published a test page to demonstrate what your browser's audio fingerprint looks like.