Before President Bush visited London last month, the English press indulged in frenzied speculation about the extraordinary security measures that would be taken to protect him. The papers fretted about a number of humdrum potential hassles (street closures, monstrous traffic jams), but they also raised a more peculiar concern: Would the government of Britain selectively block cell-phone signals along President Bush's route? If they did—whether they switched off the cellular networks along his path or jammed local cell-phone signals—nearby mobile phones would become inoperable.
As it turns out, they didn't jam cell phones. But this arcane-sounding precaution was no figment of the English imagination. Cell-phone jammers—already available on the Internet to security honchos and average Joes alike—are a surprisingly useful (and widely used) tool, and they could easily become as popular as cell phones themselves.
A cellular "security bubble" in London could have protected Bush from a very real threat: terrorists who use cell phones to detonate bombs from miles away, or even another country. By connecting a cell phone to hidden explosives, and then calling that phone, one can detonate a bomb (the electrical charge that activates the ringer on the cell phone serves as the triggering signal). In May 2002, Palestinian militants in Tel Aviv nearly caused a major explosion when they placed a bomb wired to a cell phone in a fuel truck headed for Israel's largest fuel depot. (The bomb detonated, but the fire was put out.)
The physics of jamming a cell phone are actually quite simple. Cell phones operate by sending signals along a range of the electromagnetic spectrum reserved for their use. (In the United States that part typically is measured as either 800 or 1,900 megahertz; in Europe it's usually 900 or 1,800 megahertz.) All a cell-phone jamming device needs to do is broadcast a signal on those same frequencies, and it will interfere with any devices trying to transmit in that range. The net effect for a hapless cell-phone user? The phone's screen will simply indicate that no signal is available. Odds are most people won't even notice that their phones are being jammed. They'll just assume that they're in a dead spot—and feel annoyed.
It is possible for intrepid consumers to acquire the same technology that's used to create security bubbles around traveling dignitaries. Sites offer a wide range of jamming devices at reasonable prices. For instance, the SH066PL2A/B is a portable cell-phone jammer that sells for 169.99 British pounds ($293). The SH066PL2A/B will get you a security bubble of about 30 feet, and it's camouflaged to look like a cell phone, so you can leave it out on a restaurant table and no one will know you're the source of the blissful silence in the room.
Those seeking a more robust alternative can purchase a bigger device, which will cover a radius of about 100 feet. Law-enforcement officers use the big jammers to cut off mobile communication in volatile situations, isolating hostage-takers and other baddies from the outside world. And corporate security folks can use them to thwart innovative industrial spies, who have several neat new tricks. These days, a boardroom Mata Hari can purchase a specially designed cell phone that will answer incoming calls while appearing to be switched off. In a business meeting, she could casually leave her phone on the table while excusing herself to go to the bathroom. Once she's gone, she can call the phone she left behind and eavesdrop on what the other side is saying in her absence. Sound farfetched? Perhaps, but this threat is the marketing hook for a new product, the Netline Cellular Activity Analyzer, which supposedly can detect hidden cell phones in a room. The same logic calls for installing a cell-phone jammer as well, to ensure you have complete privacy in your offices, or at least in conference rooms where important negotiations occur.
But there's a problem.
In the United States, actively jamming a cell-phone signal is illegal. The FCC, which is the government agency in charge of regulating the airwaves, has established severe penalties for doing so. If you're caught at your local restaurant with the SH066PL2A/B, it's possible you could face an $11,000 fine and a one-year jail term. Possible, but apparently highly unlikely. It seems that the FCC has never charged anyone with this crime, even though the American market is one of the most important when it comes to selling cell-phone jamming equipment. One distributor (who wished to remain anonymous) told me they've exported approximately 300 jammers to the United States this year, more than to any other country. The exporter claims that buyers include restaurants, schools (including some universities, which have installed the technology to stop students from wirelessly diddling away on their phones during lectures), and personal users.
According to the FCC, cell-phone jammers should remain illegal. Since commercial enterprises have purchased the rights to the spectrum, the argument goes, jamming their signals is a kind of property theft. But there are countries with less draconian rules. France, for instance, seems to turn a blind eye to the active use of cell-phone jammers in movie theaters, and countries such as China, Russia, and Israel either permit use of these technologies, or are very lax when it comes to enforcing restrictions.
Americans seeking a legal way to jam cell phones can look into "passive" jamming technologies. For instance, lining your office in lead should ensure that no signals get in or out. But if lead is too industrial to suit your décor, a more genteel alternative exists: You could install "magnetic wood" paneling throughout. A Japanese scientist, Hideo Oka, has invented a new kind of building material, saturated with magnetic particles made of nickel-zinc ferrite that supposedly deflect 97 percent of mobile-phone signals.