Lisa Winckler, global director of research and technology at CPFilms, argues that the film has applications beyond simply blocking Wi-Fi signals, which are transmitted in the same unregulated 2.4-gigahertz band that is used by many cordless handsets. By shielding against signals across a wide swath of the electromagnetic spectrum, including the near-infrared, Signal Defense film can also thwart eavesdropping technology that depends on transmissions in the near-infrared, or terahertz range.
"With the advent of laser microphones," explains Winckler, "you can pick up voice data [through a window]. It's done every day in government."
Born of the Cold War
Many of these more exotic applications—including blocking the stray transmissions of keyboards, old-style televisions and computer monitors, and even LCD flat-panel displays—originated in the military's so-called TEMPEST program. TEMPEST was a code name for an initially classified effort to determine whether foreign governments could extract useful information from recordings of the stray electromagnetic noise generated by electronic devices. (In the first unclassified paper on the subject, published in 1985, Wim van Eck, then a researcher at Neher Laboratories in the Netherlands, demonstrated that it was possible to use a wireless antenna to reproduce the image on a television screen even when they were separated by a wall.)
"There was a huge movement in the government several years ago for TEMPEST protection," says Arthur Money, who was an assistant secretary of defense from 1999 to 2001 and has since become a consultant for defense contractors, including CPFilms. As a result, according to computer security expert Schneier, the government covered the windows of the National Security Agency's headquarters with a fine metallic mesh, and sandwiched metallic shielding between its wallboards.
In contrast to these early efforts, Signal Defense Film has the advantage of being inconspicuous. It is transparent to over 50 percent of the light that shines on it, "which is a lot," says Winckler, CPFilms's chief of research and development. "Sunglasses are always less than 5 percent transmission…. You could put this on the glass in an office building and most people would come in on Monday morning and not know it was there."
CPFilms's Davies sees applications for Signal Defense Film in everything from hospitals, which now have obligations under the federal Health Insurance Portability and Accountability Act (HIPAA) to keep patients' records private, to the financial sector, where interior conference rooms might benefit from being shielded from electronic eavesdropping.
"Retailers are trying to make their environments more appealing by letting in more light," says Davies, "but in doing so they're also allowing more information to flow through the glass."
As Networks Proliferate, So Does Noise
As the number of wireless networks and devices multiplies, even individuals who aren't worried about security stand to benefit from increased electromagnetic shielding.
"We have had conversations with buildings, especially high-rise buildings where there is a lot of signal going on at the upper floors of those buildings," Winckler says. When the ambient signal from transmission towers, other networks and even microwave ovens becomes overwhelming, shielding a building can improve the performance of any wireless networks within its walls.
Starting in 2009 even some cars will have their own wireless networks. "Over time, you can imagine," former defense official Money speculates, "if you had cars stacked up at a stoplight, the amount of interference is potentially horrific. This film will probably be in every car window just to keep interference down, let alone for privacy reasons."