

Why Snowden Asked Visitors in Hong Kong to Refrigerate Their Phones - srivast
http://thelede.blogs.nytimes.com/2013/06/25/why-snowdens-visitors-put-their-phones-in-the-fridge/

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wdavidlee
(Full disclosure: I work at Colorado Sensors)

Intentionally building a Faraday cage is really hard.

The major radiation leaks are caused by non-conducting joints at edges of the
enclosure. If there are penetrations (e.g., power lines, signal coax,
compressor coils, thermocouple wires) then extraordinary measures must be
taken to ensure that electro-magnetic radiation remains inside.

It took me about a year to develop a narrow band Faraday cage that achieved >
120dB of attenuation. The secret sauce was gaskets made of Indium and tuned-
stub interferometers on each feedthrough.

A typical refrigerator door has a gasket seal that forms a lovely slot
antenna. I have a 0dBm transmitter in my kitchen refrigerator that easily
communicates with a symmetric receiver in the basement. The link loss is no
more than 30dB. (Online demo at
[http://www.coloradosensors.com](http://www.coloradosensors.com)).

TL;DR Refrigerators keep cold air in, but let E&M waves out.

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devindotcom
I'm pretty sure they tested this out and modern refrigerators don't act as
Faraday cages:

[http://mentalfloss.com/article/51597/does-refrigerator-
make-...](http://mentalfloss.com/article/51597/does-refrigerator-make-good-
faraday-cage)

Older ones might have been lead-lined or otherwise different; you might have
better results with a microwave. That said, it's a pretty good guarantee that
the phones are not surreptitiously recording a conversation.

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egwynn
I think a lot of us already saw the various other sources debunking the
fridge-as-faraday-cage theory. That said, low temperatures do increase the
internal resistance of batteries. If you put your phone in the freezer for a
while (probably not a great idea due to the high ambient moisture) then it
will turn off, and not turn back on. A little bit later, it'll probably tell
you that it can't turn on because of low battery. But once it's back up to
room temperature, it should turn on just fine (again, assuming the moisture in
the freezer hasn't screwed it up really badly).

Blocking radio signals is one thing, but using a fridge might have been an
effective way to deactivate most off-the-shelf batteries in a non-invasive and
impermanent way. Does anyone think this idea has any merit?

