Time-Reversal Acoustics

And once again, I find Thursday a source of fascinating, but currently, practically useless tech knowledge.

Knock 3 Times on the Ceiling (to Turn on the DVD Player) by Anne Eisenberg (NYTimes, 1 July 2004).

This article describes how ordinary tables, windows, and other solid objects can be used to control electronic devices through the use of time-reversal acoustics technology. The article gives several ideas about how such technology might be used, but I haven't yet figured out how it's going to apply to my life.