Apple has applied for a patent in which a mechanism is proposed that would allow external sound, for example traffic noise that would otherwise be blocked by headphones, to pass through to the listener.

The patent application says, in part, "This external sound can be presented to users via the same interface, channel, or audio-output device used to present audio-media. External sound can be blended ... with audible media and/or it may be presented as it occurs (live) and/or stored so that it can be subsequently presented as recorded. External sound can be stored independent of the media presentation in accordance with, for example, various events, user input, or any other programmable criteria."

Various methods of manipulating and controlling this external sound source are described. For example, the external sound could be recorded and replayed.

The motivation may be hinted at in this part of the patent description: "As a result, users of the audio devices can conveniently switch between external sound and audible media ... without having to take headphones off."

Some states in the U.S. prohibit driving while wearing dual headphones. This patent could lead the way to a technical solution in which drivers can become aware of external sounds and, eventually, via revised legislation, become exempt from removing their headphones/earbuds while driving.