A curious incident on the Smashing Security podcast highlights an often-overlooked privacy risk. A listener named Matt found that his Bluetooth headphones would not switch over to his phone. The culprit turned out to be a single AliExpress webpage left open in his browser. The page was playing nothing audible — at zero volume — yet his headphones could still hear it.
The explanation is that websites can embed silent audio tracks that are inaudible to human ears but still detectable by nearby microphones. In this case, the signal from the open webpage was enough to keep the headphones connected, interfering with the normal switch to the phone. The same technique can be used for tracking, as the podcast's title suggests: a silent audio signal from a webpage can be picked up by other devices, potentially linking a user's browsing session to their location or other hardware.
The incident is a concrete example of how tracking can operate outside human perception. It also shows a practical side effect: the silent audio interfered with the user's own device. While the episode does not detail the full extent of such tracking, it serves as a reminder that seemingly inert browser tabs can still be doing something in the background.