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In the movie Kingsmen, there is a poison which behaves differently from most other poisons.

It has to be ingested in order to kill, but that is not enough. It is harmless until a radio signal is broadcast close to the victim, which causes death in a few seconds. This allows spies and assassins to do things such as timing their victims' deaths, or negotiating mercy in exchange for info.

Is it possible to make such a poison with current technology, or at least with technology expected to be available within the next decade?

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    $\begingroup$ This is a good example of asking about something from a third-party world in a world building context. $\endgroup$ – JBH Jun 3 '19 at 4:24
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    $\begingroup$ @JBH And yet the question got plenty of upvotes, excellent answers and comments, and no one was hurt. Great question, great answers, great commentary, OP got the info they need, no problem here. ...........................Except for one person pedantically pointing out an arbitrary "rule" for no reason. $\endgroup$ – user91988 Jun 3 '19 at 17:22
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    $\begingroup$ @only_pro I don't think JBH was being pedantic or speaking against this question. I took his comment as a compliment to the question. $\endgroup$ – The Square-Cube Law Jun 3 '19 at 17:36
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    $\begingroup$ Anything radio is susceptible to interference, "... including interference that may cause undesired operation." $\endgroup$ – Mazura Jun 3 '19 at 18:10
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    $\begingroup$ @only_pro I think eveyone misunderstood. This is a great example of the proper way to ask a world-building question involving a third-party world. My comment is in support of Renan's question and in support of the examples provided in the Meta question for permitting these kinds of questions. $\endgroup$ – JBH Jun 3 '19 at 18:36

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A radio activated pill about 15mm long by 5mm diameter would probably do the trick.

The human body is fairly transparent to 100MHz radio signals. The speed of light in human tissues and fluids is roughly 1/6th that of free space. Therefore the wavelength of a 100MHz signal passing through the human digestive tissues and fluids would be roughly c / 100MHz / 6 = 50cm (as opposed to 300cm in air).

A receiving antenna typically needs to be 1/4th wavelength, which in this case is 12.5 cm.

Construct a pill having an inner enclosure. An antenna made of 12.5cm of 30 gauge enameled spring wire, and a gelatin outer coating.

enter image description here

The antenna spring wire wants to spring into a straight position, but is coiled around the inner chamber and held in place by a gelatin coating. You would need to wrap the antenna 12.5cm / 5mm / pi = 8 times around the body of the 5mm diameter capsule to get the required length.

When the pill is ingested the gelatin dissolves and the spring wire extends to its naturally straight position. The human stomach is about 12 inches long so there is more than enough room for a 12cm antenna to extend.

The body of the inner capsule contains two electrodes. One made of aluminum and the other made of copper oxide (you can pick any other two metals if you wish). When the gelatin outer coating dissolves and the electrodes are exposed to stomach acid they will form an aluminum copper battery that will power the receiver. Prior to being exposed the battery will have no electrolyte and will remain inactive.

The inner chamber is sealed and contains a small low-voltage ASIC chip, a small charge of gunpowder, and the required poison. Upon receiving the signal the chip will use the charge in the battery to ignite the gunpowder thus releasing the poison.

Or You could bluff
Create a poison pill with a coating that dissolves in a certain amount of time. The amount of time it takes the stomach acid to dissolve the coating would be proportional to the thickness of the coating.

Based on your knowledge of how the time release mechanism works you have a good guess of when the victim will fall ill. A little before the appointed time you watch closely for signs that your victim is being affected. Your well trained eye allows you to see the effects before others notice it. Then announce that you are going to trigger the poison. Pull out your remote and conspicuously press the button. Soon afterwards the victim dies. Everyone assumes it was you.

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  • $\begingroup$ This seems like a reasonable proposal, but you've got a problem: what stops the body from trying to digest the pill as other food would be digested? I don't know about you, but the idea of something that long and (relatively) rigid getting into the intestines strikes me as having a lot of potential for fatal medical complications (namely poking holes in the intestines, or blocking them) without any poison required. How are you going to keep the pill from moving past the stomach, exactly? $\endgroup$ – Palarran Jun 6 '19 at 12:20
  • $\begingroup$ @Palarran There are various plastics and coatings that are indigestible. The enamel on the antenna and the sealed part of the inner capsule would be made of such materials. Though stomach acid can dissolve the metal in the battery terminals, it takes more hours than the pill would actually be in the digestive system. With respect to the antenna, it is made of 30 AWG spring wire. Floating freely in a fluid the antenna will try and straighten, but it 30 AWG spring wire will easily bend if pushed by anything. $\endgroup$ – user4574 Jun 6 '19 at 12:51
  • $\begingroup$ If the antenna can be relied upon to bend with the rather lengthy path of the intestines (as opposed to getting lodged in there), then it will effectively be shortened: you're going to lose the ability to reliably pick up the relevant radio signal, even if that's less relevant after it leaves the stomach. That also puts you on a time limit: the spy or assassin has only until the pill escapes the stomach to achieve their aim. Still, there is no such thing as one-solution-fits-all, and this is not automatically a bad thing: complications and drawbacks make excellent sources for drama in a story! $\endgroup$ – Palarran Jun 7 '19 at 2:32
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The big problem here is wavelength. Radiowaves have relatively long wavelengths and are best received by macroscopic metal antennae. On the scale of individual molecules, you simply won't get enough energy absorbed to see any actual changes. "Oh, but what about microwaves?" I imagine someone saying. Well, microwaves work by imparting energy to polar solvents, like water. If you have to microwave someone in order to make the poison work, you're probably going to have to heat them up in a very painful and probably fatal way which isn't going to be at all subtle and you may as well use instead of faffing about with poison.

Visible light has a short enough wavelength that it can impart a decent amount of energy to matter (have a think about why visible light is visible in the first place) but humans are largely opaque to visible light. The combination of "imparts enough energy to matter to cause interesting chemical changes" and "penetrates human bodies" gets you x-rays and gamma rays, and if you can subtly irradiate someone with large doses of ionising radiation then you can probably dispense with the poison bit and just zap them to death.

Existing approaches to using magnetic or electromagnetic means of affecting materials in a human body also won't do what you want. The magnetic nanoparticles linked by L. Dutch aren't changed by the magnetic field, just pulled into the right location. This means you'd need to dose someone with something extremely toxic that stays resident in the system and hope that it doesn't kill them before you give them a massage with a big magnet.

There's another neat trick using visible light to trigger preprogrammed genetic effects, called optogenetics which is closer to what you want, but in order to make it work you need to surgically implant a load of LEDs or fibre optics in your target, which is also awkward (to say the least).

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    $\begingroup$ How big does a radio antenna have to be? Could you disguise one in pill form? $\endgroup$ – Arcanist Lupus Jun 4 '19 at 0:31
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    $\begingroup$ @jpmc26 I'm also not entirely sure how plausbile x-ray activated chemistry is; there is such a thing as "too much power" after all. $\endgroup$ – Starfish Prime Jun 4 '19 at 18:17
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    $\begingroup$ @jpmc26 Impacting chemistry is easy. My comment was more about whether xray exposure can cause reliable and repeatable changes in a target chemical, or whether an x-ray beam that could pass through a human body would be more likely to just randomly smash it up or partially ionise bits of it you'd rather leave as they were. $\endgroup$ – Starfish Prime Jun 4 '19 at 21:44
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    $\begingroup$ @StarfishPrime it varies with the wavelength; BLE and WiFi frequencies are attenuated fairly heavily. However, with a device inside the body, there’s the potential for coupling to the body to transmit, I’m not sure if that helps in this scenario, but a quick google shows a paper using 2.4Ghz for localisation within the body. They note that propagation varies in different tissues. They also highlight the MICS band 402-405Mhz dedicated for transmission to implanted devices. essay.utwente.nl/66071/1/Dove_MA_TE.pdf $\endgroup$ – Dan W Jun 5 '19 at 17:37
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    $\begingroup$ @StarfishPrime It should be noted that the required antenna length would be a lot lower than normal inside the human body because of the high dielectric constant of the tissues and fluids. Also, an antenna can be made shorter than its optimal size and still receive a signal (it will just be less efficient). But with the right receiver you can pick up very weak signals. I personally did a set of experiments where I sent a 10mW 13MHz (23m) sinewave and picked up the signal about 20 feet away using a loop antenna of 1 foot diameter and a small resonating capacitor. $\endgroup$ – user4574 Jun 6 '19 at 4:07
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Targeted delivery of drugs has already been demonstrated by using nanoparticles and magnetic fields (source).

Therefore it is plausible to think of nanoparticles which are activated or concentrated by an EM signal.

I.e. one could inject the nanoparticle below the toxicity threshold, and a magnetic or electromagnetic field could be used to locally concentrate them above the toxicity threshold. It could be a fantastic chemotherapy or a lethal poison.

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    $\begingroup$ You can get chemistry to fluoresce with EM, too. That's just another kind of trigger. I think it's more than plausible to develop a radiologically-activated poison. It almost makes me wonder why the world hasn't. It would keep people on the no-fly list on the ground. $\endgroup$ – JBH Jun 3 '19 at 4:22
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    $\begingroup$ @JBH - because finding things that are both non-toxic and lingering but can be made toxic without any additional chemicals, just energy, is extremely non-trivial. (Also, finding such a chemical which also responds exclusively to a EM spectrum not present in nature - not many of those - compounds the difficulty.) $\endgroup$ – jdunlop Jun 3 '19 at 7:09
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    $\begingroup$ The problem in this case is that you either need very powerful magnetic fields ("and all he has to do is to step into this MRI machine and he is doomed! muhahaha") or weak magnetic fields of the sort that a victim might be exposed to anyway ("sorry boss, he was given a new magnetic buckyball toy and activated the posion before he'd had a chance to read the blackmail demands"). And you really have to hope that no other process concentrates the poison in any way (kidneys and liver, I'm looking at you).] $\endgroup$ – Starfish Prime Jun 3 '19 at 11:03
  • $\begingroup$ @jdunlop, Ah, JD! If it was easy it wouldn't be any fun! Gratefully, we're not being asked to provide such a formula (not that we're not all on the Homeland Security watchlist already anyway). $\endgroup$ – JBH Jun 3 '19 at 15:00
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    $\begingroup$ @JBH How so? Are you proposing poisoning everyone on the no-fly list, and killing any that come into contact with radiation? $\endgroup$ – Acccumulation Jun 3 '19 at 16:15
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RFID chips can now be produced in sizes below 200 µm. That's below "grain of salt" size, and could be embedded in any food or beverage expected to contain coarse texture. These are active electronic components that can report or respond to unique digital signals. On top of that, all you need is a low-power micro-mechanical mechanism to release the actual poison from a sealed container, gated on receipt of matching data payload. The energy to release could be mostly chemical energy, rather than from the RF, with a tiny amount of energy from RF source merely as the activation.

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    $\begingroup$ An anonymous user tried to inappropriately edit in this: "Information above is incorrect. 200 µm is the thickness not the overall size. Hitachi holds the record for the smallest RFID chip, at 0.05 mm × 0.05 mm. A major challenge is the attachment of antennas, thus limiting read range to only millimeters." 0.05 mm is 50μm. $\endgroup$ – R.. GitHub STOP HELPING ICE Jun 4 '19 at 12:02
  • $\begingroup$ Indeed there are serious challenges making the antenna work but it's an area of current advancement. The proposed size corresponds to low THz bands and can plausibly travel a few meters in air and can penetrate somewhat, but not well, in human tissue. So you'd probably want it to lodge near surface of body. $\endgroup$ – R.. GitHub STOP HELPING ICE Jun 4 '19 at 12:09
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Microwave radiation could, possibly, be used to initiate a polymerisation reaction by agitating water buffered organic monomers. A large enough mass polymerisation event could create lethal blockages of small blood vessels throughout the body. There are major problems with this idea though:

  • The chemicals in question are not going to linger in the body for all that long, the human body is pretty good at breaking down or flushing out unwanted organic compounds. So your poisoning window is probably only going to be 48 hours at most.

  • Given the level of microwave background radiation in our modern environment low levels of polymerisation are going to start immediately exacerbating the decay of the poison's potential efficacy, and also introducing the slim possibility of a lethal "misfire".

  • The dose of radiation needed to create a mass polymerisation that is definitely going to be lethal is going to be very high, you'd probably need to point a long range communication antennae at the person you want to kill at which point the poison is, if some things I've heard are to be believed, superfluous and regardless makes it rather impractical.

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  • $\begingroup$ "So your poisoning window is probably only going to be 48 hours at most." I'm ok with that, but your two other points are really strong against the feasibility of such a thing. $\endgroup$ – The Square-Cube Law Jun 3 '19 at 12:38
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    $\begingroup$ Just to be clear, are you saying that the radiation dose required to trigger this effect would in itself cause death by radiation poisoning? $\endgroup$ – Muuski Jun 3 '19 at 15:00
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    $\begingroup$ @Muuski I'm not sure that being boiled by microwaves is quite the same as what people traditionally call "radiation poisoning", but technically I suppose it is ;-) $\endgroup$ – Starfish Prime Jun 3 '19 at 15:15
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    $\begingroup$ @Muuski More would boil the target alive in their own skin. $\endgroup$ – Ash Jun 3 '19 at 16:32
  • $\begingroup$ @Renan Yeah you might be able to do something with either a different wavelength or by using a compound that is sensitive to sound rather than EM but I'm not sure those would work where as a water buffered compound would. $\endgroup$ – Ash Jun 4 '19 at 13:30
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Nanites

A poison itself, not so much but a poison delivery system where nanites can release the poison on command would work.

Currently scientists are working on a nanite delivery system for cancer drugs.

Alternately you could forget the poison and just have buzzsaw nanites that just start cutting on command.

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    $\begingroup$ Y'know, I think this is one of those rare situations where the answer "just assemble a whole load of nanoscale robots that can evade the immune system" is, in fact, the easier and more sensible approach. $\endgroup$ – Starfish Prime Jun 3 '19 at 11:00
  • $\begingroup$ @StarfishPrime And I never thought I'd hear that described as "more sensible". Still, despite the neat trick with the U-bend hose in the training section, this isn't generally a film you watch for its realism and lack of plot holes. :) $\endgroup$ – Graham Jun 4 '19 at 7:35
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Resonance Sensitive Membrane

One may develop an artificial microorganism (nanite or nanoparticle) that has a cellular membrane which is sensitive to a particular frequency of radio waves.

Just like an opera singer breaks a glass by matching its resonant frequency, these microorganisms' membrane will rupture under the suitable radio waves, thus releasing the deadly poison or virus or bacteria or whatever you like, that is trapped inside it.

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    $\begingroup$ You're gonna have scale problems. You can't use radiowaves for that, because the particles are too small compared to their wavelengths. You can use visible light, but the wavelengths of light that are powerful enough to impart actual chemical changes are too short to penetrate the human body. $\endgroup$ – Starfish Prime Jun 3 '19 at 10:59
  • $\begingroup$ Exactly as Starfish explains, all sci-fi scenes where we contact nano-particles using "radio" - are totally impossible. $\endgroup$ – Fattie Jun 3 '19 at 14:41
  • $\begingroup$ @StarfishPrime I agree, in that case, it won't work. Can we not use some kind of EM waves or some minor non-lethal radiation. $\endgroup$ – V.Aggarwal Jun 4 '19 at 3:31
  • $\begingroup$ @V.Aggarwal Probably not with an organic carrier perhaps with something artificial, perhaps a capsule that opens when subjected to a pulsed signal in the X-Ray spectrum. Once advantage of this would also be that the pulsed signal could encode a specific activation key this would greatly reduce the risk of accidental activation by other technology such as medical X-Ray machines etc. Though you couldn't really easily feed them enough energy to power the mechanism this way, probably a bit sci-fi for the time scale but using an organic/inorganic hybrid that uses metabolism to provide the energy. $\endgroup$ – MttJocy Jun 4 '19 at 16:01
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A sub-dermal capsule seems the best solution. Poison dart frog poison is functional in extremely tiny doses so a small bb with an electro-mechanical release seems plausible with not needing much range/penetration on RF signal. There are certain ceramics out there you can drill with the smallest drill you can find then heat shrink down smaller. This is used in some chip manufacture. Small poison bb's were supposedly used by the secret police in either NAZI Germany or old USSR I can't remember which.

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Many answers already are great, but I think they don't really go for what you really want. As I read it, you want this poison to only be triggered when you want. Current solutions described are poison triggered by a radio signal, but not "triggered by only THAT ONE radio signal". So your victim will just die when going too close to a radio emitter, or an electric induction cooking system. So by only reacting to a particular wavelength, you will be fearing any EM noise. Still works if in a controlled environment, but clearly not as in the movie.

To get something to react to a heavily encrypted radio signal with our current tech, I am afraid that you will need some electronic parts in your poison, so a releasing capsule seems to correspond the best. Either ingested or inoculated. So it will be easier to detect and to get out of the system.

It still seems possible to expect some high end lab dedicated to the task to get some result with a biological entity reacting differently depending on signal received (Some studies show different reactions to music in plants), but going from no symptoms to lethal with specifically that one signal, it seems far fetched. And from a potential victim point of view, it's not that bad.

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    $\begingroup$ The hypothetical magic poison does get you two things that the capsule doesn't... one, it is potentially easier to administer, and two whilst it may appear on a post mortem toxicology screen, the capsule will definitely be findable and deeply suspicious and possibly even incriminating. $\endgroup$ – Starfish Prime Jun 3 '19 at 13:39
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    $\begingroup$ (but yes, in order to respond to a specific signal, this is what you're going to need, so have a +1) $\endgroup$ – Starfish Prime Jun 3 '19 at 13:40
  • $\begingroup$ thanks. The question didn't ask for discretion, and in the movie, once poison as reached enough of the population, a TV announcement from the culprit is broadcasted, and people begin to turn blue (well, it's a movie villain plot). So yeah, the only part that can't be made "as in the movie" is that it is incorporated in cocaine and assimilated as a powder, which go back to the nanobot stuff. but being incriminating isn't in the spectre, and I would rather see OP leave a track if he poison me. $\endgroup$ – ncalep Jun 3 '19 at 15:19
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YES.
Why? Because we can kill people with "radio" waves already. People living near power lines get cancer California sources. Microwaves can cause problems. So we know that Non-Ionizing Electromagnetic Radiation can kill you. Just slowly.
So the poison would actually be just Catalysis. Something that mixed with oxygen in blood or acid in stomach AND exposed to radiation will react in way that would kill the host. We know that microwaves can boil water. Not enough energy in protons to brake O-H bond but, well, boiling water inside someone head is enough.
So if you can make the chemicals more sensitive to FM (which is closest in length to microwaves) you can create something that could be used as such poison.

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    $\begingroup$ Citations sorely needed. Powerlines cause cancer? Chemical substances sensitive to ridiculously low power FM waves? $\endgroup$ – AlexP Jun 3 '19 at 8:37
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    $\begingroup$ Important quotes from the linked study: "Our findings did not clearly support an increased childhood leukaemia risk associated with close proximity" and "Reports of increased risk for distances beyond 50 m were not replicated." (emphasis mine) This isn't a great study to support your claims! $\endgroup$ – Starfish Prime Jun 3 '19 at 11:06
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    $\begingroup$ This is a shockingly poor answer from someone of your reputation level, I must say. $\endgroup$ – F1Krazy Jun 4 '19 at 15:22
  • $\begingroup$ "boiling water inside someone head is enough." I feel like at some point you stopped talking about the radio poison from Kingsman and switched to the giant microwave from Kick Ass. $\endgroup$ – DarthFennec Jun 4 '19 at 19:26

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