Before a dinner of pizza and fried chicken late Sunday in Hong Kong, Edward J. Snowden insisted that a group of lawyers advising him in the Chinese territory “hide their cellphones in the refrigerator of the home where he was staying, to block any eavesdropping,” as my colleague Keith Bradsher reported.
Why a refrigerator? The answer does not, as some might assume, have anything to do with temperature. In fact, it does not matter particularly if the refrigerator was plugged in. It is the materials that make up refrigerator walls that could potentially turn them into anti-eavesdropping devices.
“What you want to do is block the radio signals which could be used to transmit voice data, and block the audio altogether,” Adam Harvey, a designer specializing in countersurveillance products explained. Refrigerators made from metal with thick insulation could potentially do both, he says, regardless of whether it is mild or icy within.
On the data-transmission front, thick metal walls can create a sort of electromagnetic barrier, which enables the device to function as something known as a Faraday cage. A true Faraday cage is a space where radio waves cannot pass and therefore data cannot be transmitted. Although not all fridges function this way, those constructed with more metal have the potential to serve this purpose.
Another household object that functions similarly, Mr. Harvey has learned through his research into cellphone data transmission, is a stainless steel martini shaker.
“It’s a perfect Faraday cage – it will block all radio signals unless you decide you need to pour yourself a martini,” he said. Although this sounds like a plot point in a James Bond movie, Mr. Harvey has actually done extensive tests on the shaker in the process of developing a surveillance-blocking cellphone case called the OFF Pocket.