So I was thinking about the future and some practical technology that would come with it, and I thought of this technology that would come in handy on airplanes and movie theaters.

Basically the movie theater presentation rooms would be equipped with some kind of device that would turn all the phones in the room on silent mode, or on airplanes would turn all the phones in flight mode.

My question is: could this type of technology be accomplished and what would be the legal ramifications of it?

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    $\begingroup$ These devices already exists. They block the signals. $\endgroup$
    – Vincent
    Mar 25, 2018 at 15:49
  • $\begingroup$ @Vincent I'm not talking about blocking signals just the noise the phone makes, I can't see movie theaters legally blocking signals in their presentation rooms $\endgroup$
    – Amoeba
    Mar 25, 2018 at 15:51
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    $\begingroup$ As @Vicent said, devices which block GSM signals already exist and are routinely used in more or less sensitive locations. There are no legal ramifications; there is no law which says that the owner of a house has to let third-party elecromagnetic waves pass unhidered through their house. (This is not legal advice. I am not a lawyer. Always consult a lawyer for legal advice.) The usual way to do it is to have a device which pretends to be a GSM cell; all phones flock to it, because it has the stronger signal, but the device does not connect to the backbone network. $\endgroup$
    – AlexP
    Mar 25, 2018 at 15:52
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    $\begingroup$ Ah, I see. What you want is called unauthenticated third party access. Devices which allow such access are considered defective, because they pose a gigantic security risk. Currently movie theaters etc. use autonomous intelligent devices called "security agents" which use kind words and physical force to remove the offending phone together with its inconsiderate owner. $\endgroup$
    – AlexP
    Mar 25, 2018 at 15:57
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    $\begingroup$ Several buildings from 1970's at least in Italy have wall and ceiling reinforcements using something called "Standard Welded Mesh". Which often has the side effect of turning rooms and entire buildings into Faraday cages where no cell signal can be received, unless you stand near a window. The system is completely passive, and of course 100% legal (you are under no obligation to allow radio waves inside a building). $\endgroup$
    – LSerni
    Mar 25, 2018 at 23:46

2 Answers 2


The Tech Already Exists

The THOR system in use by US forces is a phone signal jammer to prevent cell phone and radio initiated IED detonations. Basically what it does is detect radio signals and identify the troughs and peaks of the frequency wavelength, it then modulates its output to produce a peak where the detected frequencies trough is, and a trough where the detected signals peak is, only at a LOT higher power output. To explain it with a metaphor, if you were trying to talk to somebody and I stood behind you repeating everything you said only slightly out of sync and at a full scream then you would be unable to speak to anybody. Basically the same concept, the cellular and radio devices are not able to identify and translate the frequency into anything useful through all the noise.

They are quite small, the THOR pictured here is actually the last gen system, the new MJOLNIR system is about 1/3rd the size at the same power output. They have a line of sight limitation as walls and stuff stop them from working, but with no obstructions systems like this have an effective range of several hundred meters.

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As far as legal ramifications, they aren't really allowed to be used within the US because of regulations by the FCC. They can potentially interfere with emergency equipment, sensitive electronics, emergency responder radio traffic, and life saving medical devices like pace makers. They pump out a LOT of power, if you wear one for too long you get a splitting head ache from the radio frequencies resonating water molecules inside your body. The larger ones like the CREW system deployed on vehicles can black-out transmissions at up to a kilometer and if you touch the antenna while it is operating like I did on accident once you will get a radiation burn on your hand and all the skin will peel off after a few days. The biggest legal ramifications of such a system in commercial use are liability related. High power High frequency RF transmissions are nothing to mess around with. This is primarily why the FCC regulates which frequencies and power outputs can be used in certain places and for certain applications.

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    $\begingroup$ Your metaphor is spot on, in fact, it's a real thing en.wikipedia.org/wiki/Delayed_Auditory_Feedback. It causes stuttering and loss of concentration. Speech jammer is another popular term. $\endgroup$ Mar 26, 2018 at 14:56
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    $\begingroup$ I carried a THOR system on my back through 2 years worth of combat patrols, knowing how they worked was a pretty important part of not exploding. $\endgroup$
    – TCAT117
    Mar 26, 2018 at 15:27

Not quite a technology, but a convenient legal framework - just mandate by law that each mobile device must have a backdoor that listens to a prearranged signal and obeys the (perhaps only a limited set of) commands.

Note that government mandated weaknesses or backdoors are not uncommon, so it is just a matter of approving the law if the public is distracted or indifferent enough and this can happen quite plausibly in our world.

  • $\begingroup$ This is the obvious answer. $\endgroup$
    – RonJohn
    Mar 25, 2018 at 17:04

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