>Ray Dillinger wrote:
>>  If you get two sensitive microphones in a room, you
>> should be able to do interferometry to get the exact locations
>> on a keyboard of keystrokes from the sound of someone typing.
>> I guess three would be better, but with some reasonable
>> assumptions about keys being coplanar or on a surface of known
>> curvature, two would do it.  Interesting possibilities.
>>                                 Bear
>> [A quick contemplation of the wavelength of the sounds in question
>> would put an end to that speculation I suspect. --Perry]

We hear low-frequency sounds when we type.  But have we ever checked 
for high-frequency sounds outside of human hearing range?  I'd bet 
a keyboard has a number of squeaks and ticks and twangs up there.
I'd also bet that most of the keys, after a keyboard's broken in, 
don't sound exactly alike -- wear and tear, typing patterns, etc. 
You might be able to resolve ambiguities of interferometry by using 
the sounds of the keys themselves. 



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