Tempest devices could via intercepting from far away the electro-magnetic waves coming out from one's computer detect what one does on the computer. Employing the Faraday cage principle, one could prevent such detections. A. Stanoyevitch in his book Discrete Structures with Contemporary Applications, CRC Press, 2011, p.301 writes:

"Buildings can be fitted using a special insulation procedure that protects against tempest devices, but any company or individual in the US who has this insulation must first obtain a license from the federal Government."

Could this be true? If yes, which laws are involved in this context?

  • Are you asking if one must obtain a federal license to use a certain kind of insulation, and what laws would mandate this? Does the insulation have a name? Does Stanoyevitch indicate from whom the license must be obtained? It sounds pretty sketchy to me, but I couldn't definitively tell you that it was impossible, although I've never heard of such a proposal until now. It sounds more like a conspiracy theory.
    – ohwilleke
    Commented Apr 3, 2017 at 12:46
  • I don't know whether there is a standard specific name of performing such a kind of insulation. Thus I used the wordings above. A Faraday cage is another possibility. (BTW to my knowledge there are also Faraday bags to be purchased for shielding one's mobile phone such that one's location couldn't be tracked, etc.) What I quoted is essentially all what Stannoyevitch tells in the present context. I personally think that the probability of a conspiracy theory is not high, in view of the serious nature of the book and the status of the author etc. Commented Apr 4, 2017 at 7:53
  • I think that user6726 has come up with the most plausible answer.
    – ohwilleke
    Commented Apr 4, 2017 at 14:16

2 Answers 2


The only applicable law for the US would seem to be FCC regulations against interfering with "any radio communications of any station licensed or authorized". Marriott Hotels was fined substantially for blocking people's hotspots within the hotel. As I understand "tempest device", this is a method of obtaining information from stray EMR from computers and the like, which picks up on radiation emitted from a device. Stray radiation is not licensed communication. The problem would be if a room were insulated to block all EM radiation coming in or going out, including licensed transmissions. The main enforcement interest of FCC is with devices that actively jam signals (by transmitting interference). But the law, 47 USC 333, states that "No person shall willfully or maliciously interfere with or cause interference to any radio communications of any station licensed or authorized by or under this chapter or operated by the United States Government". Insulating a room from incoming licensed radio signals is thus not allowed, under a "what the law says" reading of the law. However, laws are frequently interpreted in terms of beliefs about an intent, so it's possible that a court could eventually decide that the law was not intended to prevent construction of a Faraday cage room. The issue would then be whether an intentional action to do something allowed which has an (unintended) disallowed but non-harmful consequence would be deemed a violation (the user would be okay with blocking licensed transmissions into the room). I don't know of clearly applicable case law on that point.

  • My layman's question: You wrote: "Insulating a room ....is thus not allowed". Could one say that this is generally true (since the government does have its own radio broadcasting)? If so, then an authority could arbitrarily (i.e. only in cases it wishes) make use of that argument, with the consequence that anybody must first apply for a permission from the authority before doing any insulation work, isn't it? Commented Apr 3, 2017 at 19:26
  • FCC "interference" I'm pretty sure is defined specifically to mean active energy sources. And it seems a technique designed to stop the unintentional signal used by tempest would not be "willful or maliciously" blocking communication.
    – user4460
    Commented Apr 3, 2017 at 21:33
  • Employing such insulation could be suspected to be because one has some criminal matters to hide. I learned elsewhere that "US Code / Title 18 - Crimes and Criminal Procedures / Part 1 - Crimes / Chapter 119, 2510 to 2521" could thus apply. What's your opinion on that? I also learned that, analogous to what you mentioned, there are building codes that require the communications of the fire services be not blocked, thus defecto ban the insulation IMHO. Commented Apr 4, 2017 at 7:30
  • I don't know about the properties of such insulation, so it is possible that it's also a code violation. The 'interception' laws would actually apply to tempest devices, and not to protection against them. With a warrant, police could legally use such devices to detect criminal activity, but it would not be illegal to thwart interception with insulation.
    – user6726
    Commented Apr 4, 2017 at 14:41

A Faraday cage can prevent EM emissions that can (in theory) be used to eavesdrop on electronic devices. But no, there is no U.S. law against putting metallic screens around a room or within a building. Just as there is no U.S. law against putting shades in windows that would prevent visual surveillance of anything inside.

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