There was talk on HN 25 days ago about a "Mysterious Mac and PC malware that jumps airgaps?" [1]. Looks like you could use something like this to implement it.

[1] https://news.ycombinator.com/item?id=6646936

...and now you know why the DoD uses portable SCIFs when handling TS/SCI in the field[1].

[1] http://www.bbc.co.uk/news/world-us-canada-12810675

I sense a new STIG -- system shall not have acoustic generation capability of any kind, or microphones of any kind. ;)

Watch out for seemingly unrelated sensors. A few years ago a friend was showing off his Macbook Pro, with harddrive accelerometer picking (IIRC) faint traces of normal speech.

Ah, and good luck with removing sound capabilities from smartphones ;-)

Reminds me of the dtrace guys screaming at their storage array while observing some disk metrics live, and seeing a clear spike.. http://dtrace.org/blogs/brendan/2008/12/31/unusual-disk-late...