SIGNAL DEFENSE FILM blocks a wide swath of the electromagnetic spectrum, but is nearly transparent to visible light.
©CPFilms

When a Boeing 757 struck the Pentagon on September 11, 2001, a blastproof film on its windows prevented them from shattering into a swarm of flying shards. Now, a version of that same film promises to block not only projectiles but also the collective electromagnetic chatter generated by our increasingly wireless society.

Once manufactured under an exclusive contract with the U.S. government, this recently declassified window film is now available to the public. But don't expect to see it on store shelves anytime soon. Currently, it's only available directly from the manufacturer, and at prices that will likely make it prohibitive for all but the wealthiest home owners.

The coating, which in its thinnest incarnation is only two one thousandths of an inch thick, can block Wi-Fi signals, cell phone transmissions, even the near-infrared, yet is almost transparent, making it no more intrusive than conventional window treatments. It can keep signals in (preventing attempts to spy on electronic communications) or out, minimizing radio interference and even the fabled electronics-destroying electromagnetic pulse (EMP) generated by a nuclear blast.

The film has already been plastered across the windows of more than 200 government buildings, including structures operated by the departments of Defense and the Treasury, as well as in the homes of high-level members of the current administration.

"We are limited by confidentiality agreements to say exactly which buildings [the window film] is on," says Kent Davies, president of CPFilms, Inc., in Martinsville, Va., which manufacturers the protective covering dubbed LLumar Signal Defense Security Film. "But immediately after 9/11 one of the senior military officials talked about a window film that seriously protected against the damage from the plane crash. You can put two and two together and assume it was also protecting against wireless signals."

But Is It for You?

Unlike the built-in security measures present in nearly all wireless routers, Signal Defense Film doesn't come cheap. CPFilms declined to give details of their pricing structure, in part because their technology is only sold as part of an all-inclusive package (of which the film is one component).

In addition, some experts are skeptical whether there is—or should be—a market for the film outside of the government and large corporations.

"If you're military, sure, it's useful. But if you're a normal person, it's kind of dumb," says Bruce Schneier, a consultant and authority in the fields of cryptography and computer security. "The way you secure wireless is [by securing your computer]—this is the wrong point to apply the solution." Without means of encryption and software-based security, he asserts, "you're out in the open anyway." Schneier himself is so confident in his ability to secure his computers that he runs a completely open wireless network in his home.

On the other hand, despite the widespread availability of wireless security features, many organizations and individuals have failed to secure their networks. In 2005, for instance, hackers broke into the wireless network of a Marshalls department store by using an antenna to remotely intercept its transmissions. Using this access as a starting point they managed to steal more than 200 million credit card numbers from a central database of customer information. The wireless network they breached was protected by Wireless Encryption Protocol (WEP), an older standard whose weak encryption can be cracked in under two minutes.

An internal audit revealed that the chain did not move quickly enough to convert its networks to the stronger Wireless Protected Access (WPA) standard. When the plot was finally uncovered, TJX, Marshalls's parent company, hired dozens of investigators and offered to pay for fraud monitoring for customers whose data was stolen.