THIS IS A TEST of the Galactic Emergency Alert system

No action is required.

Type: Milkyway Empire

The World

In the near future:

  • we discover FTL
  • we run into some friendly aliens that are part of a benevolent galactic "empire"
  • in order to join, we must have a global emergency alert system that can reach >95% of our population

Most areas can be covered by cell phone/tv/radio alerts.

It is getting the alert out to the remote areas that concerns me

"remote areas"

  • Areas without cell service and no other alert method (radio,etc)
  • Areas with a warning system that we can't automate/hook into
  • Areas without a warning system at all (and no radio/etc.)
  • Areas without electricity

Partial Solution

I believe we can mass produce a simple pole with

  • antennae
  • Raspberry Pi
  • solar panels
  • batteries
  • loudspeakers

I can see deploying these in remote areas via B-52. The pole is dropped, it will jam itself into the ground and activate (pole is designed to manage terminal velocity)


Including manufacturing time, how long would it take to ensure that >95% of the population would hear the global alert?

Assume that all major countries want to contribute.(The empire has a LOT of benefits when we join)

  • 18
    $\begingroup$ It might be cheaper, easier and have many unrelated benefits to invest into a proper permanent GSM network. Global mobile phone ownership is on the rise, especially in developing countries. 95% of the world population either owning a mobile or having someone nearby with one isn't unrealistic in the near future, especially when governments would be willing to subsidize them. $\endgroup$
    – Philipp
    Commented Oct 3, 2018 at 19:43
  • 4
    $\begingroup$ vaguely related, Hughes is working on a system that relies on LEO satellites to provide internet to everyone by 2027 oneweb and Elon Musk/Space-x seems to have a similar idea called starlink $\endgroup$
    – depperm
    Commented Oct 3, 2018 at 19:54
  • 19
    $\begingroup$ Would methods of reducing the rural population be acceptable? Giving everyone a free cellphone and building out a global cell network is the boring approach. Killing everyone we can’t reach with existing systems would be a more novel and interesting solution, if it’s permissible. (I mean, you floated the idea of dropping speaker poles into remote areas from B52 bombers... why not just drop bombs?) $\endgroup$ Commented Oct 4, 2018 at 0:26
  • 27
    $\begingroup$ Given that over 5% of the world's population is apparently deaf, I think it will be hard to create an effective system using loudspeakers $\endgroup$
    – A C
    Commented Oct 4, 2018 at 5:02
  • 12
    $\begingroup$ Why not ask the benevolent galactic "empire" how they do it? They will probably appreciate your efforts at compatibility with their systems. $\endgroup$ Commented Oct 4, 2018 at 11:46

10 Answers 10


Reduce the Population

95% gets a lot easier if you can chop off the long tail. Now that you can move things faster than the speed of light, kinetic kill weapons can devestate the world. While world leaders debate how to achieve the goal, a rogue faction secedes to the moon, cracks the earth in half, and neatly qualifies for entry into the galactic fold. Then, they emigrate somewhere nicer than this galactic backwater.

  • 2
    $\begingroup$ I agree, the rogue faction that enacts this plan will be highly immoral. $\endgroup$
    – Daniel B
    Commented Oct 4, 2018 at 1:28
  • 10
    $\begingroup$ But take note, I have to emphasize this, this is highly logical. Immoral, yes, but logically correct. $\endgroup$
    – Mr.J
    Commented Oct 4, 2018 at 1:30
  • 3
    $\begingroup$ @Mr.J , etc. - I'm already killing off at least 50% of the population at the end of "Chapter 1" because of a massive multi-brood infestation of Space Locus in our asteroid belt. I don't want/need any more needless killings. ( worldbuilding.stackexchange.com/questions/102010/… ) $\endgroup$ Commented Oct 4, 2018 at 1:35
  • 5
    $\begingroup$ @MichaelKutz You forgot to add that detail, this changes things. If your period is post apocalypse, do you think most of earths facilities are still intact? $\endgroup$
    – Mr.J
    Commented Oct 4, 2018 at 1:57
  • 5
    $\begingroup$ The problem is that killing off the people in remote places is much harder than killing all the people in Tokyo, Shanghai, and Jakata (which is about 0.1 billion). Apart from anything else, people in remote places often live much more self-reliant lifestyles, so a collapse of civilization will tend affect them less. $\endgroup$ Commented Oct 4, 2018 at 11:02

First off, >95% coverage means that, with a worldwide population of 7 billion, you can ignore 350 million people. Which I feel like gives you some wiggle room.

Second, when you say 'near future,' what do you mean?

If you mean anything longer than the next few years, you may not need to do anything other than use cell phones. As of 2017, about 70% of the world's population owned one, and that percentage is rapidly increasing. In many areas of the world, mobile phones are the way you access the internet.

Additionally, about a quarter of the world's population is under 14 years old. The vast majority of these children, I believe it's safe to say, will be within hearing distance of an adult.

So, 70% of the world has cell phones. 25% are close enough to an adult to hear one in an emergency. Adding those together gives you 95% coverage.

Now, that's cutting it a little close as of 2017, but with the increasing ubiquity of mobile devices, I don't think it's unreasonable to assume in your 'near future' scenario that more than 95% could hear a cell phone if it went off.

But what if you wanted to be even more sure? Well, as we're all aware, humans are not evenly distributed across the planet. China and India each have more than a billion people, and many of those are among the poorest in the world... and they also live in large cities. By hooking up your raspberry pi to some airhorns in those large cities, you can pick up whole percentage points of the world population.

Want to be even more sure? Require phone manufacturers to donate a few tens of millions of devices, for the good of the planet. Ship those devices to every village in Africa and rural community in India, and voila! Even better coverage.

So, even assuming you're not happy with the current growth of cell phone usage worldwide, which within the next few years will easily take you over 95% coverage, manufacturing and shipping those cheap mobile devices for rural areas would take, what, a year? At most? We're already making hundreds of millions of phones now, so it wouldn't take long to redirect them where they're needed if necessary.

  • 39
    $\begingroup$ What percent of cell-phone users are also under 14 years old? I agree with the validity of the rest of your answer, but if there's any chance of overlap between two groups, you can't get an absolute percent, just lower and upper limits. $\endgroup$
    – DqwertyC
    Commented Oct 3, 2018 at 23:53
  • 15
    $\begingroup$ I think that you are mixing things up with the percentage addition part, kids with phones will not cancel out with kids out of ear shot, those two categories will actually both decrease the percentage. $\endgroup$
    – vero
    Commented Oct 4, 2018 at 7:52
  • 2
    $\begingroup$ As far as I know even villages in Africa usually have a few cellphones in them. The users often have to go to the next city to get a connection, but many have one. There's even a pretty popular payment method there that uses SMS. $\endgroup$ Commented Oct 4, 2018 at 9:52
  • 2
    $\begingroup$ @DqwertyC Considering the rate at which cell ownership is increasing, I think it's fair to say that overlap won't matter within a few years. I don't have any hard numbers to calculate it out, though. $\endgroup$
    – anon
    Commented Oct 4, 2018 at 19:25
  • 1
    $\begingroup$ Shipping the devices isn't the problem, coverage and airtime is the issue. A lot of backwater Africa villages have at least one cellphone if not more. The people will barter for airtime and then travel to a coverage area to call family etc. If we shot up satellite's that could transmit emergency alerts and standardized the protocol and communication methods to target 95%+ we would achieve it with current technology. $\endgroup$ Commented Oct 5, 2018 at 19:01

Detonating nukes in very high altitudes causes a lot of noise and brings along some nice pyrotechnical effects:

In general, nuclear effects in space (or very high altitudes) have a qualitatively different display. While an atmospheric nuclear explosion has a characteristic mushroom-shaped cloud, high-altitude and space explosions tend to manifest a spherical 'cloud,' reminiscent of other space-based explosions until distorted by Earth's magnetic field, and the charged particles resulting from the blast can cross hemispheres to create an auroral display which has led documentary maker Peter Kuran to characterize these detonations as 'the rainbow bombs'.

If we have the tech for FTL, we have the tech to blow some nuclear fireworks up high. That should gather a lot of attention. We could do it around the globe.

  • 60
    $\begingroup$ Your attention please. An emergency has been declared. Nuclear explosives have been detonated in your atmosphere to draw your attention to this emergency. Incidentally, it is also the emergency itself. $\endgroup$
    – Cort Ammon
    Commented Oct 3, 2018 at 20:37
  • 14
    $\begingroup$ You had me at "detonating nukes". $\endgroup$ Commented Oct 3, 2018 at 22:12
  • 3
    $\begingroup$ This is killing 95% of the world's population, IN STYLE. $\endgroup$
    – Mr.J
    Commented Oct 4, 2018 at 2:52
  • 6
    $\begingroup$ Wouldn't the EMP kill all electronics everywhere? Some might consider that a negative. $\endgroup$ Commented Oct 4, 2018 at 6:01
  • 6
    $\begingroup$ Welp, If the cause of emergency may be fatal to us humans, then I might as well die while seeing a nuclear blast by my naked eyes and a fooking aura in the sky!!! That would be an icing on the cake. $\endgroup$ Commented Oct 4, 2018 at 12:25

Is the scope of the system to only be on Earth? If that is the case, then satellites should suffice, as we have had 100% coverage for decades now. The old Iridium constellation, famous for its satellite flares, was able to completely cover the Earth, as shown below:

enter image description here

Simply use a satellite alert system for phones, or use those pole thingies you mentioned but hook them up to a satellite.

  • $\begingroup$ But how long would it take to manufacture and distribute the pole thingies to ensure >95% of the people can be reached? $\endgroup$ Commented Oct 3, 2018 at 21:30
  • 3
    $\begingroup$ @MichaelKutz Depends how dedicated you are. I doubt if we have FTL travel greater than 5% of the population would be disconnected from the internet, so this question may not even be applicable. $\endgroup$ Commented Oct 3, 2018 at 22:08
  • 3
    $\begingroup$ Iridium is still going and launching new satellites. $\endgroup$
    – Schwern
    Commented Oct 4, 2018 at 3:07
  • $\begingroup$ The only real issue with using Satellites is that they have trouble connecting if there is too much between you and the sky - but, that's mostly an issue in urban settings (tall buildings, etc) where we already have phone masts. Mandate a change of all phones to support both satellites and masts (since the necessary antenna are different), then run a global "subsidised trade-in" scheme to encourage everyone to upgrade (the new "basic model" might be free with any trade-in) $\endgroup$ Commented Oct 4, 2018 at 7:31
  • 2
    $\begingroup$ @MichaelKutz If money is no object (and lets face it, you're joining an intergalactic community here, it's worth shelling out!) then you could probably contract a few manufacturers and churn out a few million of the things in a matter of months at most. $\endgroup$
    – Ruadhan
    Commented Oct 4, 2018 at 11:34

Low Frequency Radio

Remember those radio-controlled clocks? They get the current time from a radio signal. The entire United States is covered by one broadcast tower in Fort Collins, Colorado. It operates on 60 kHz band. This tower broadcasts at 1 bit per second, but you could presumably increase the baud rate a bit...

What you would do is give every citizen a little device that would listen for this broadcast. This antenna could also be placed in cell phones, clocks (duh), and other devices. So for the technophobes that don't want phones or whatever you could use that arduino setup you mentioned, deploying them in strategic areas, instead of all over the world.

As for the broadcast towers, to build in redundancy, I'd go with two per continent.

As for the message, unless you want to ignore the 1 bit per second part, it could just say "get to a tv/radio/Internet access point!"


Induced Gravitational Harmonics

You didn't mention if you have artificial gravity to go with your FTL or not, but if you do, and depending on how it works, inducing fluctuations in the planet's natural gravity at a frequency audible to humans could make every loose object on the entire planet vibrate out your message all at once.

As a bonus, more targeted manipulation could be used to crush flat anyone who doesn't want to join the galactic empire.

Solar Thermal Transducer

If you don't have sufficient artificial gravity power to pull this off, set up a solar laser array. Pumping a few gigawats of thermal energy into the atmosphere at the proper frequency and dispersement pattern should let you create arbitrarily loud sounds at arbitrary points on the planet's surface. You'd just have to keep your message short to avoid, shall we say, unpleasant side-effects...

As a bonus, any dissidents who don't want to join the galactic empire can simply be vaporized in the middle of the night. No muss, no fuss, no witnesses!


There is a school near where I live that is less than a mile from a 50,000 watt radio transmitter station. As it turns out, you'd be amazed what kinds of things can be used as AM receivers if the signal is strong enough... Lockers, desks, telephone lines, people's fillings... Anything conductive and capable of vibrating is potentially susceptible to being driven by a sufficiently powerful signal. The energy budget to blanket the globe this way is probably cost-prohibitive given that you'd have to convert it to radio waves, and the damage it might do to sensitive electronics would also be expensive, so the other options are likely better.

  • 1
    $\begingroup$ Sounds similar to how the Vogons announced their intentions to destroy earth to make way for a hyperspace lane. But, how do you overcome the multiple Language barrier? $\endgroup$ Commented Oct 5, 2018 at 1:56
  • $\begingroup$ @Michael Kutz Why not simply repeating the signal in every known language ? $\endgroup$ Commented Oct 5, 2018 at 12:47
  • $\begingroup$ @MichaelKutz The technical requirement is for the message to "reach" 95% of the population... That doesn't necessarily require that they understand it. But you could use multiple languages for the messages if you want to be nice. $\endgroup$
    – Perkins
    Commented Oct 5, 2018 at 19:15
  • $\begingroup$ @Perkins just send a black-and-white skull and crossbones flag :P $\endgroup$ Commented Mar 12, 2021 at 22:57

What about projecting the message on the moon? Everybody can see it, you only need one powerful enough projector rather than a global installation, you can cover the costs through ads.

The problem however would be language and the fact that the message would not be instantanious for everybody.

Or instead of projecting on the moon, set up a (or multiple) sufficiently large screen(s) in higher orbit and project on those.

  • $\begingroup$ The moon would be too small. It's not that big of a screen. Also any screen that could be visible from the night sky as described could also be used as a weapon to block out the sun. $\endgroup$
    – HSchmale
    Commented Oct 5, 2018 at 14:01
  • $\begingroup$ The moon is big enough, but that is also the problem. "One powerful enough projector" has to outshine the Sun (!). Your worst-case scenarion is the full moon, in which the visible disk of the moon is fully lit by direct sunlight, unattenuated by any atmosphere. $\endgroup$
    – MSalters
    Commented Oct 5, 2018 at 14:12
  • 1
    $\begingroup$ The power requirements are something of a hurdle here, what-if.xkcd.com/13 $\endgroup$
    – Bomaz
    Commented Oct 5, 2018 at 16:05
  • 1
    $\begingroup$ @bomaz - GMTA :) $\endgroup$
    – Fattie
    Commented Oct 5, 2018 at 19:14
  • 1
    $\begingroup$ Projecting the image onto the moon would require ridiculous power, but putting down a few billion "pixels" on the surface that can be changed between reflective and non-reflective would work during the full moon, and they could be illuminated brightly enough to be visible during the new moon relatively cheaply compared to a projector. A solar array of similar size on the back side should be sufficiently large. For bonus points, name the construction effort "Project disco ball". $\endgroup$
    – Perkins
    Commented Oct 8, 2018 at 18:05

Regarding the viability of purchasing a phone for every person in the world:

https://www.nbim.no/no/ - 8 468 829 792 352 nok (about a trillion dollars)

That is the savings of Norway, a small european country of 5 million people. That is more than enough to buy a smartphone for the last 30% of the world who are still disconnected from the internet.

I am sure we could figure something out.

  • 2
    $\begingroup$ The Norwegian state savings are hardly typical as its the result of squirrelling away oil money for the last 30+ years. Norway may be a small country - but its has vast natural resources. $\endgroup$
    – papirtiger
    Commented Oct 5, 2018 at 17:03

This would be trivial with today's technology because,

Fortunately in our real world there's a near-duopoly on device OS.

Couldn't be easier. In five minutes the 2 major device OS, and the few minor device OS, could be forced to add more "emergency alert" functions than they do now.

Step 2, governments would simply mandate that older versions of the OS don't work, which is easy to achieve.

None of that is any harder then, say, that you "must have brakes on a vehicle" and so on - any regulation.

A tiny number of people don't have a device currently; it would only cost a few billion to make a minimal one for those folks.

Note that a few nutters would want to avoid being contacted: your 95% rule easily covers that case.

Easy! Thanks to the current duopoly on device operating systems.

  • $\begingroup$ I don't think that the roughly 65% of Android users that aren't using some version of 8.0 will be happy that they will need to buy new phones. A lot of people don't upgrade their phone until it's broken, and a lot of Android manufacturers stop updating older and cheaper models after only a year or 2. However, it would be a LOT simpler to just have the government develop a couple of apps that are compatible with all version and force the manufacturers to push a non-removable version of that app to the phone similar to how some manufacturers force Facebook or TripAdvisor on their phone. $\endgroup$
    – Nzall
    Commented Jan 14, 2019 at 10:04

There seems to be two assumptions that people are making that I want to unpick:

  1. That a warning signal must be in a spoken language.

  2. That "urgency" means getting the message to people in minutes rather than days.

Put a set of nuclear-powered satellites in low-earth orbit, such that their orbits cover the globe. Fit each with an incredibly a bright light source - perhaps an array of thousands and thousands of LEDs?

Take the time to contact the hard-to-reach population areas the slow way - by mail or in person - and tell them where to look in the sky each night for the signal. Give them training on what action they should take if they see the emergency light.


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