Faraday Sleeves For Phones

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Now, I have it on good authority that a proper Faraday cage needs to be grounded for optimal performance, and a sleeve like this obviously isn't grounded, but that doesn't mean that it won't block signals to/from your phone well enough to increase your privacy. It depends on a variety of things so your mileage may vary, but it's certainly an interesting option to keep in mind if you're trying to find a balance between the convenience of having a cell phone and the privacy of not being tracked or listened to surreptitiously.