Aspects of this Idea already exist in terms of interfering with the functionality of pacemakers. It seems to me, though, that it should be possible to send an electromagnetic signal that is specifically tuned for the nervous system to directly receive it. We know that the nervous system can conduct small amounts of actual electricity, which means that nerve-axons should be able to act like antenna....
Late last year I personally had a significant heartbeat-error problem (more details about that in a bit), and I only have guesses regarding how it started to go haywire like that. Anyway, I've been back to normal for several months now, and have reason to think the problem won't spontaneously recur.
WHILE that problem existed, however, over the course of several months, I gained more than 25 kilograms of weight, all of it fluid. At the time I thought a dietary problem was the cause, which could be fixed by changing my diet, but nothing worked. Note that I basically FELT fine the whole time, except with respect to physical awkwardness associated with trying to move unaccustomed weight around, and swollen legs and belly that didn't want to bend easily, and stuff like that. When I finally went to the hospital, they took several days to finally figure out what the cause of the problem was. At the hospital they literally drained out 10 whole liters of fluid, and could have drained more (but they opted to use diuretics to get rid of the remainder).
Anyway, somehow 3 chambers of my heart were beating at twice the normal rate, and the 4th chamber was trying to beat at twice THAT rate. That is pretty-much a sure-fire way to wear out one's ticker early, but the side-effect, fluid loss from the circulatory system and consequent body-swelling, led to catching it before it was too late. The heart doctor used some shock treatment to reset the heartbeat to the normal rate, and like I said, I've been back to normal since.
SO, I have first-hand knowledge about heartbeats getting messed up, and don't want to see uninformed annotations here to the effect that I don't know what I'm talking about, in terms of that aspect of this overall Idea. There are also, if you don't know already, medical cases in which someone received a moderate blow to the chest, and then died because the heart stopped (see link).
I'm imagining a weapon designed to deliberately mess up the heartbeat of an enemy, using an electromagnetic pulse of the proper frequency, or possibly a specially-timed sequence of pulses. You definitely want these pulses to be aimed/projected away from you!
Early versions of the weapon might need to have a sensitive electromagnetic-energy receiver (like a remote EEG device), to detect the heartbeat, so that the interference-pulses are properly mismatched with normal nervous-system beat-signals.
Later versions of the weapon might be powerful enough, to not care what the current state of the heart is, during its beat- cycle. Imagine a souped-up version aimed at an entire enemy army. When fired, every heart stops, but the soldiers won't know it immediately. The impact of the electromagnet pules(s) is painless. They will, however, all fall down about 15-30 seconds later, because no fresh oxygenated blood is reaching their brains; they will basically fall unconscious. Painlessly, remember. About 6 minutes later, the whole enemy army is brain dead, and will be completely dead some time after that (muscle cells take a lot longer to die from lack of oxygen than brain cells).
To defend against this weapon, you might have to wear a Faraday Cage (link). Or, perhaps all you need is a pacemaker protected by a Faraday Cage, so that if your heart is remotely stopped, it can detect it and restart the beats.
In terms of the local scene, the investigators studying the corpse now have a dilemma. Did death occur because the heart stopped? Yes. But was the stoppage natural, or was it the result of a remote command (murder)? How can they tell???
Probably, somebody is going to have to put some radio receiver/recorders at every cell-phone tower in the country, to detect and triangulate heart-stoppage pulses. Murderers won't be able to get away with it. But the army might like it, along with any government looking for a painless method of executing criminals.-- Vernon, Jun 26 2015 Sudden death http://www.ncbi.nlm...gov/pubmed/17229310As mentioned in the main text. [Vernon, Jun 26 2015] Faraday cage https://en.wikipedi...g/wiki/Faraday_cageAs mentioned in the main text. [Vernon, Jun 26 2015] //I've been back to normal for several months now// It's OK - nobody suspects.-- MaxwellBuchanan, Jun 26 2015 I knew the arrhythmia would come in handy some day...-- 2 fries shy of a happy meal, Jun 27 2015 random, halfbakery