"Search for a perfect cellphone muffler
It could happen on a train, in a restaurant or during an awe-inspiring aria （咏叹调） at a performance of ""Carmen"": A neighbor's cellphone starts bleating （叫 / 响） the theme song from ""Friends,"" disrupting the 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 （无法运作）in certain locations. Methods include jammers （干扰发射台）that interfere with the phones' frequencies, routing systems that mute their 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 legal restrictions.
The concerns go beyond mere annoyance: Casinos are seeking to stop phone-based cheating; prison authorities want to guard against phone use by inmates for drug deals or other forms of wrongdoing. With the rise of camera cellphones have come privacy concerns that have made locker rooms （更衣室）and other areas no-phone zones.
Dave Derosier, chief executive of Cell Block Technologies, based in Fairfax, Virginia, is developing a transmitter the size of a smoke detector that relays （发射）signals of ""no service"" to cellphone frequencies, prompting them to send calls to voice mail.
Cell Block's products are slightly more sophisticated versions of what is probably the most widespread method of stopping cellphone use, called jamming, which renders phones inoperable by disrupting the connection between cellphone towers and the phones. Jamming devices overpower phones' frequencies with strong signals and often with loud noise.
The jammers range from $200 for a rudimentary hand-held model to nearly $10,000 for suitcase-sized gear sold to governments and the military.
Other means are also in development, from devices that detect the use of cellphones (and prompt users to desist 终止) to construction methods that render them inoperable.
But not everyone finds this trend encouraging. Cellphone industry experts and federal regulators deride jammers in particular as unlawful, unethical and even dangerous.
""You're not allowed to barricade the street in front of your house because you don't like hearing an ambulance,"" said Travis Larson, a spokesman for the Cellular Telephone Industry Association, who asserts that blocking systems inhibit customers' rights and can block emergency calls. ""Just like roads, the airwaves are public property.""
Derosier said that devices like those made by Cell Block are ""questionably legal"" in the United States, but he added that with proper disclosure and provisions made for emergencies, there is no reason that they should not be used. The devices are legal in Japan, France and Eastern Europe, and in most of South Asia, Africa and the Middle East, he said.
Meanwhile, others have begun devising ring-restriction technology that is unquestionably legal. Bluelinx, based in Charlotte, North Carolina, is developing a system called Q-Zone (the Q standing for quiet) that uses Bluetooth wireless technology （蓝牙无线技术）- in transmitters and embedded into cellphones - to put phones equipped with Q-Zone software into silent or vibrate mode when they are taken into a specified zone. Jeff Griffin, Bluelinx's president, said he was trying to sign up wireless providers and establishments like cafés and theaters. He said he hopes to start using the equipment in the next few years. Unlike jammers, he said, his call-blocking system would be optional for cellphone users, who could turn it on or off.
""I was at church some time ago and a lady's cellphone went off and the entire church froze,"" Griffin said. ""Meanwhile, she couldn't find her phone and was so embarrassed. It's that kind of circumstance we're trying to fix."" A similar system is being developed by Stefan Marti and Chris Schmandt, researchers at the Massachusetts Institute of Technology's Media Lab. Their project, called Autonomous Interactive Intermediaries, uses technology like speech recognition to screen calls to determine when a phone should ring, and subtle, silent visual cues to replace cellphone rings or vibrations. Marti pointed out that the technology, which could become available within four years, can always be overridden by users.
Larson of the cellular industry group said that while the industry objected to controls imposed on cellphone ringing, it did not oppose measures left to the customers' discretion.
Another means of guarding against disturbance is the use of detectors, sold legally in the United States and abroad, that sound an alert when a cellphone is present. Zetron, a company in Redmond, Washington, makes the Cellphone Detector Plus, a $449 receiver that sounds an audio alert when it detects certain cellphone frequencies. The model, about the size of a thermostat （自动调温器）, flashes a red light, beeps and plays a recording that urges people to turn their phones off.
An Israeli company, Netline, makes a detector called the Cellular Activity Analyzer, a hand-held device that is used to monitor and detect cellular communication activity in a given area. (It is offered at www.netline.co.il or www.spyshops.ca for $2,500.) Smaller detector models include the RF Signal Detector from Suresafe Technology, about the size of a beeper, which costs less than $100.
A different, legal approach is to block cellphone signals through construction techniques. Like most blocking methods, many of these ideas were developed long ago for military and espionage （间谍）purposes, said Bill Sewell, senior vice president of DMJM Technology, who has spent years designing radio-secure areas for the U.S. government. Sewell said the methods used by his firm are simple: Metal mesh screens tuned to the frequencies of radio waves are mounted inside the wall. They are inexpensive, at about $15 a square foot, he said.
Like Sewell, Deborah Chung, a professor of materials research at the State University of New York at Buffalo, has developed construction materials that block radio waves. Her ""smart concrete"" contains electrically conductive mixtures, like metal or carbon particles, that provide electromagnetic interference.
Her structures are designed for the military and hospitals, she said, but they could be used in other structures to keep cellphone users away. ""It certainly would work,"" she said. ""On the other hand, they might not be able to watch TV inside.""
By Sam Lubell April 10, 2004