It could happen on a train, in a restaurant or during an awe-inspiring aria at a performance of ?Carmen?: a neighbour?s cellphone starts bleating theme song from ?Friends,? disrupting mood and setting nerves on edge. Wouldn?t it be great, you think to yourself, if this couldn?t happen?



Others are thinking likewise, including companies and researchers developing or already selling devices that render cellphones inoperable in certain locations. Methods include jammers that interfere with cellphone frequencies, routing systems that mute phones? ringers in specific places, sensors that detect active cellphones and building materials that block cellphone waves. Proponents say that such measures are more effective than ?no cellphone? signs, ?quiet cars? on trains or even legal restrictions.



Dave Derosier, CEO of Cell Block, says it is developing a transmitter that relays signals of ?no service? to cell frequencies, prompting them to send calls to voice mail. Cell Block?s products are more sophisticated versions of most widespread method of stopping cellphone use, called jamming, which renders phones inoperable by disrupting connections between towers and cellphones. Such devices can be found on eBay and at Websites.



However, experts deride jammers in particular as unlawful, unethical and even dangerous. Others have begun devising cellphone ring-restriction technology that is legal, at least until further notice.



Bluelinx is developing a system called Q-Zone (the Q standing for quiet) that uses Bluetooth wireless technology ? in transmitters and imbedded into cellphones - to put phones equipped with Q-Zone software into silent or vibrate mode when they are in a specified zone. Jeff Griffin, Bluelinx?s president hopes to start using the equipment in next few years.



A similar system is being developed by Stefan Marti and Chris Schmandt of MIT?s Media Lab. Their project uses technology like speech recognition to screen calls to determine when a phone should ring, and even subtle, silent visual cues to replace cellphone rings or vibrations - say, an animatronic rabbit or parrot turning toward you in a room to signal a call.

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