The other week, the New York Times reported that NSA whistleblower Edward Snowden was understandably cautious about planning his departure from Hong Kong to Russia (emphasis mine):
“It was a cloak-and-dagger affair. Mr. Snowden wore a cap and sunglasses and insisted that the assembled lawyers hide their cellphones in the refrigerator of the home where he was staying, to block any eavesdropping. Then began a two-hour conversation during which Mr. Snowden was deeply dismayed to learn that he could spend years in prison without access to a computer during litigation over whether he would be granted asylum here or surrendered to the United States.
Wait. What? Why are the cellphones getting chilled? Snowden’s idea, presumably, was that the refrigerator would act as a Faraday cage. As I explained last year when talking about the effectiveness of tin foil helmets, a Faraday cage is an enclosure made up of a conducting material that shields its interior from external electrostatic charges and electromagnetic radiation by distributing them around its exterior and dissipating them. While these enclosures are sometimes actual cages, they come in many forms, and most of us have probably dealt with one type or another. The scan rooms that MRI machines sit in and the shielding on USB cables, for example, both provide protection as Faraday cages. Inside such a cage, signals to and from these lawyers’ cellphones would be blocked, preventing them from being used to surveil the meeting.
In theory, a sturdy metal fridge should make a good Faraday cage. In practice, some fridges don’t really cut a cell phone off from the rest of the world. Make magazine writer Michael Colombo tried it out with his home refrigerator, and was able to make a call to a phone inside of it. He had better results with a metal cocktail shaker.
I put my fridge to the test, too, and got the same result. Calls and data transmissions went right through. I have a glass cocktail shaker, so that's not an option for me if I'm trying to stay hidden. I wondered if there was a decent kitchen Faraday cage available to people like me, or the poor souls who have no cocktail shaker at all.
I lurked on some survivalist message boards for a while (not an activity I can recommend) and learned that a lot of doomsday hobbyists plan on relying on their microwave to protect their electronics if the government/aliens/New World Order tries to mess with them with an electromagnetic pulse. This makes sense, since, unlike a fridge, a microwave oven is actually designed specifically to shield the electromagnetic radiation of microwaves and keep them from getting out of the appliance. If electromagnetic radiation can’t get out, then it shouldn’t be able to get in either.
Sure enough, calls and data sent to my phone while it sat in my old GE microwave never went through. I could see it sitting in there, but there was no ring, no alerts. When I pulled it out, there was no missed call notification, either. So, the next time you need to keep prying eyes and ears away from your phone, your best bet seems to be tossing it in the microwave or a (metal) cocktail shaker. Just don’t forget about it when you heat up some leftovers or make a Manhattan.