Almost everyone knows there are kosher hot dogs and pickles, but you have to be a real aficionado of kosher to know that there also is such a thing as a kosher sound system. Seeing a niche market, a small Washington, D.C.area research company last year received a patent for just such a system. And in what must be a textbook example of how a new technology can be transformed into other products, the company is developing a listening device based on the same principles that would allow farmers to hear insect larvae munching away inside grain elevators.

Both applications evolved out of the same core problem: How do you make a sound system without electricity? For Orthodox Jews, the question arises in connection with the Biblical commandment not to do work on the Sabbath or other holy days. Traditionally, one definition of forbidden work was lighting a fire. In the modern age, orthodox rabbis have taken the modern incarnation of fire to be electricity, and therefore any effort on their congregants' behalf that initiates the flow of electricity is forbidden. In practice, this means that on the Sabbath, Orthodox Jews are not allowed to turn on a light or push a floor button in an elevator. The prohibition also rules out the use of electrically driven microphones.