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This morning when I woke up, I found nobody. Literally...

All houses and cars where abandoned, as if everybody was gone in a hurry leaving everything. I took a car and drove around: nothing...

My first thought was "hey I'm finally able to finish my 'in progress' Steam game list!". But after finishing Arkham Knight (waste of time), I thought I was time to show the world I still exist, by building a huge beacon!

Criteria:

  • visible/audible from very far
  • any standard human could deactivate it, to show it found me!
  • long-lasting for years
  • it should be self-sustainable, for example it should keep running when I go hunting for food cans or exploring other cities for several hours/days

Settings:

  • present day
  • I live in the suburb of a great city
  • obviously I'm the only one building it. I have access to some machinery (bulldozers,...)
  • I can be any profession you want, I have a library nearby so I can learn
  • this is a post-apocalyptic scenario so I suppose there will be quite shortly a massive power outage

Is it possible? Will I finally be able to be found by somebody else?

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    $\begingroup$ If it keeps running when you are not there, it will indicate your presence even when a pack of wolves has had your for lunch... $\endgroup$
    – L.Dutch ♦
    Aug 7, 2017 at 7:01
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    $\begingroup$ If you're looking for a high-tech solution, then some (but certainly not all) of the answers to What would be the (most difficult) challenge to make a “10,000 year satellite”? on Space Exploration may be of interest. $\endgroup$
    – user
    Aug 8, 2017 at 13:54
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    $\begingroup$ Sure that's a good idea? Whatever "took" all of humanity could notice one of those annoying humans escaped... $\endgroup$
    – r41n
    Aug 8, 2017 at 14:33

11 Answers 11

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I think the best bet would be to find a civil defense siren. These are loud, designed to be heard over a large area, and low maintenance. If the siren's in your area are mechanical then you could setup a water wheel to drive it. If they're electronic then you can scavenge some solar panels. Either way this system should be pretty easy to setup and be annoying/unique enough to draw people towards it. Once the people arrive at the siren you can write in spray paint/rocks/laminated paper/etc. directions for them to turn it off. If the siren ever turns off you go to investigate if it is a maintenance issue or another survivor.

Some likely places to find them include:

  • A fire station
  • A high school pep rally supply locker (some schools use these when the home team scores a touchdown in American football games)
  • Natural disaster warning systems for flood zones, tornado or tsunami areas
  • Army/Navy surplus stores

If you don't have access to an off the shelf siren you can always build one. If you didn't know how it was done off the top of your head, you would need to go to your local library and find the Jan. 2014 issue of Make: which had an article on Air Raid Sirens. As near as I can tell this magazine's prototype siren was much like the version seen in this wikiHow article. It should be easy enough to scavenge materials to build one.

In a perfect world you'd setup the siren in a location that is heard from your home but not right under it where you'd be driven crazy by the noise.

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    $\begingroup$ Note: Since the person lives in a suburb of a big city, they should be able to find an adequately load siren already hooked up and working at the local fire station. Bonus: many fire stations have solar or other alternate energy sources to insure they still work if the power grid is down. $\endgroup$
    – RBarryYoung
    Aug 7, 2017 at 18:53
  • $\begingroup$ @RBarryYoung for sure. I've edited my answer to include some places to look. $\endgroup$
    – Erik
    Aug 8, 2017 at 19:07
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A mast with a flag will do the trick.

Build the flag with textiles you can find in the city. Preferably synthetic ones, and brightly colored. You should be able to arrange them in a fancy pattern, ensuring high visibility. (Yellow and black stripes would be fine, if it wasn't for the "danger" code they transmit)

Find or build a very high pole, place it on a high place, and rise the flag there. It will be visible from distance and will tell the world somebody with opposable thumbs lives here.

If you hang it to a non-vertical line, you will also overcome the problem of the flag being scarcely visible when there is lack of wind.

Since you are in a post apocalyptic scenario, it's hard to have people travelling during night time, thus night visibility is less of a concern.

When somebody finds it, he/she will simply lower the flag and you will know somebody found it.

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    $\begingroup$ and periodically change the flag, to show that it hasn't just been left there. $\endgroup$
    – Baldrickk
    Aug 7, 2017 at 9:40
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    $\begingroup$ Run up a bell or metal object that will strike the flagpole, too. $\endgroup$
    – Ross
    Aug 7, 2017 at 15:03
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    $\begingroup$ Why would travelers care about the flag? Why would they investigate a flag and lower it? Why wouldn't the flag just be a hold-over from when all the other people disappeared? $\endgroup$
    – Erik
    Aug 7, 2017 at 18:00
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    $\begingroup$ @Erik well, I could knitt "help" or "spaces > tabs" to draw attention $\endgroup$
    – Goufalite
    Aug 7, 2017 at 18:40
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    $\begingroup$ @Erik That's a good point--I'd say on top of buildings, maybe on radio antennae/satellite dishes/lighting rods/etc when available? Most flags are on flagpoles on the ground (at least near me) and aren't really visible from a long distance. $\endgroup$
    – MissMonicaE
    Aug 7, 2017 at 19:13
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The flag suggested by L.Dutch is great for attracting people to your place. You might also make the area around flagpole stand out from its surroundings. It could be just keeping it clean and tidy whereas everywhere else is is dusty and strewn with windblown rubbish. Having a neat, weedfree, garden with edible plants would clearly indicate recent activity. Even just a vase with cut flowers would do. Fresh flowers are obviously fresh. Flowers that are only a week or two old may be untidy but look very different to flowers left for months or years.

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you don't have to do anything. your garbage pile will indicate your presence. Burning dirty garbage such as tires will create a smoke plume and soot fallout visible from space. Also a wide ranging odor. Garbage also would have the advantage of attracting wolves, which you can then tame and use to hunt with, which, under your direction will be accomplished more efficiently than the wolves could on their own, further depredating the area and indicating your presence.

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    $\begingroup$ Welcome to the site, asdasdf. In the future, try to refrain from providing one- or two-line answers, as these are commonly considered inadequate to sufficiently answering the question. If you haven't already, feel free to take the tour to get a better understanding of the site. This post has made it into the low-quality review queue, so may be deleted. $\endgroup$
    – Frostfyre
    Aug 7, 2017 at 18:52
  • $\begingroup$ This does not provide an answer to the question. Once you have sufficient reputation you will be able to comment on any post; instead, provide answers that don't require clarification from the asker. - From Review $\endgroup$
    – L.Dutch ♦
    Aug 7, 2017 at 18:54
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    $\begingroup$ @L.Dutch Actually, I think this kind of does provide a unique, valuable answer. $\endgroup$
    – Southpaw Hare
    Aug 7, 2017 at 18:58
  • $\begingroup$ Agreed on the two above points : this question doesn't match the visible/audible from far away criteria although it can be linked to the flower answer. Can you put more information ? $\endgroup$
    – Goufalite
    Aug 7, 2017 at 18:58
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    $\begingroup$ I don't know what to do. I think the garbage fires is reasonable but I think taming wolves and training them to hunt on demand is a bit of a stretch. You'd have a better chance with feral dogs. $\endgroup$
    – Erik
    Aug 7, 2017 at 20:21
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Everyone else has disappeared, but presumably many of them have left their cars behind. So go out and collect all the car batteries you can find, and then connect them to blinking Christmas lights. String the lights around the top of the tallest building in your area (like in "28 Days Later").

If you use efficient LED lights, they should last for about a day on a fresh battery while you explore the rest of the city. (Feel free to use your library to set up a more elaborate circuit, with more batteries, for multi-day trips.) Unlike a flag, they require semi-frequent maintenance, so you won't keep attracting people to your area if you die. You can either keep stealing car batteries, or hoard gas and recharge them in their cars. (This is how they keep the radio on in Alas, Babylon. If you don't have a car of your own, the library will tell you how to hotwire one.)

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    $\begingroup$ The problem with battery is the lifespan. It would be less efficient but problably have a better durabilty to plug less LED light to a "wind electric generator" (don't know the english term) and if necessary, to a thermic engine, fuel will run out (and be less efficient with time) but this would be a back-up for days without wind. $\endgroup$
    – AxelH
    Aug 9, 2017 at 8:17
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Scavenge rock-climbing equipment from a sports shop, and as many red spray paint cans that you can find. Let yourself slide down the roof of the tallest building, and paint large red bands along its side (on all four sides preferably).Correctly prepared fires can burn a long time.

There are safety self-blocking knots which you can make to prevent yourself from falling if you faint or loose your grip (I bet your library will have some book on the topic of rock-climbing or knots). You can train and test your knots by sliding down the roof of a much smaller 1-storey building and a mattress below, so that in the even that something goes wrong, you will not get more than a bruise. For extra safety and a less precise result, you could even sellotape the nozzle of the spray can in the down position, and then lower the can with a rope without leaving the roof yourself.

At the bottom of the building, you can place a calendar where you tick the days off and leave messages saying when you intend to come back from your excursions. If you put it in the building's entrance hall, it will be shielded from the weather for a reasonable amount of time.

By using an axe and a few tools to get yourself through doors and up to the building's roof, you can probably put this plan into practice within a couple of days, without learning anything other than the rudiments of making a couple of rock-climbing knots.

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  • $\begingroup$ Welcome to WorldBuilding! Nice idea. If you have a moment please take the tour and visit the help center to learn more about the site (and earn a badge). Have fun Georges! $\endgroup$
    – Secespitus
    Aug 8, 2017 at 12:38
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If you can still play Steam games it assumes you still have electricity. Why not just put a blinking bright light on the roof of your house? Perhaps a cluster of turn-signals scavenged from cars?

I'd also consider a radio transmitter for longer range contact. Should be pretty easy to come up with something that broadcasts your location on a loop over some AM frequency..

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    $\begingroup$ The steam games was just at the beginning, I know that I have at least 24 hours of electricity. But of course, car batteries! Car batteries everywhere! $\endgroup$
    – Goufalite
    Aug 7, 2017 at 18:31
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    $\begingroup$ And there are a lot of solar panels around these days... $\endgroup$
    – Bill K
    Aug 7, 2017 at 19:23
  • $\begingroup$ Several solar panels that utilize rechargeable batteries (present day technology) plus a bright light or radio beacon was my first thought too. $\endgroup$
    – user31530
    Aug 9, 2017 at 6:02
  • $\begingroup$ Note : Batteries won't work eternally, I guess you could use the library to create some less efficient accumulator yourself. $\endgroup$
    – AxelH
    Aug 9, 2017 at 8:20
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One of the oldest signals of civilization is fire, the smoke is visible for miles during the day and the fire itself will be visible at night and it proves you are still around because it has to be fed. Set it somewhere high for added effect. Tire fires in particular burn slow and give off a lot of smoke.

As Bill K mentioned a radio transmission will work over a much wider range and allows you to provide directions and information, "I will be at X every other day around sunup". Even a simple ham radio will vastly increase the area you can signal. If you declare the day before each transmission you are proving you are not just a recording as well. You can even indicate a frequency you will be listening on for replies.

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Although medium to high maintainance required, you could try to obtain a ham radio or a ham repeater (as also suggested by Bill K) and program it to broadcast your location and maybe also a meeting point. For the electricity, you could use solar panels and buffer with lead batteries. There is certainly a building supplies store or something similar with fancy equipment for such a purpose.

Of course this approach is not usable for attracting random passers-by, but shortwave communication has the advantage that it can overcome large distances and attract the attention of may survivers at once. For mid range, you could use the very high frequency band (like normal radio stations do) since it is better traceable and only survivors in the (local) area are able to hear it. For the very short range, you could again stick to the siren or flag approach or also broadcast your "radio program" (too much fallout for me) using outdoor loudspeakers in the local area. When your station is reached by survivors, they can flip a switch to change the signal so you can notice.

Using radio communication may not be the easiest approach, but has, in my opinion, one of the best chances to meet with survivors from the semi local area and there are certainly people trying to communicate with radio as soon as the mobile networks have failed.

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Gamma-ray beacon.

Go straight to the nearest nuclear power plant -- FAST. Read all the manuals as quick as you possibly can. Intervene to stop the reactor melting down. You will now have a nuclear plant in the middle of a large territory that is expected to be a huge emitter of gamma radiation... but is not.

Gen-II reactors perform rather badly when "just abandoned" (unlike the largely vaporware Gen-III+ reactors, which only need their water tanks topped up every few days). So the expectation will be that every reactor has melted down. Rescue teams will have maps of expected ~30 mile contamination zones and ~100 mile detection zones, as well as dosimetry equipment in case the contamination zones are not shaped as expected (wind is a factor). A saved reactor will be easily detected by the lack of any increase in gamma whatsoever.

Even if observers have no idea where the nuclear plants are, they will become immediately obvious with nighttime thermal imaging. A nuclear plant will emit about the same decay heat whether it has melted down or not. It will be most peculiar on a thermal image, being a rather large structure which has odd heat sources; or in your case has heat sources from obvious structures intended to emit heat, such as a cooling tower or stack. Yours will also lack the accompanying radiation.

No one would expect a gen-II reactor to remain stable indefinitely using only on-site resources. Therefore, when search teams notice a reactor which has not cooked off, they will make it a top priority to assist there to make sure this good luck continues.

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    $\begingroup$ Thank you for your answer, but I don't think it will fit for a lambda traveller passing by the plant... $\endgroup$
    – Goufalite
    Aug 8, 2017 at 7:56
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Where's the nearest nuclear power plant? You could build a closed loop steam turbine using a fuel rod, white light LEDs will last next to forever as a night signal and the spare rotation from the turbine axle can drive an air raid siren as a daytime and an audible signal, you can have a disengagement lever that will pull the driveshaft away from the generator and shut the system down. Just make sure you use a lot of lead shielding or you gonna to die.

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    $\begingroup$ I'd advice against building anything with a fuel rod inside it - the OP wanted to signal that she or he lives, not lived there. $\endgroup$
    – Pavel
    Aug 7, 2017 at 16:45
  • $\begingroup$ Lots and lots of shielding was specified in the answer. $\endgroup$
    – Ash
    Aug 7, 2017 at 16:59
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    $\begingroup$ Are you sure about the shielding ? Randall says it is safe to swim in nuclear pools ;) $\endgroup$
    – Goufalite
    Aug 7, 2017 at 19:00
  • $\begingroup$ @Ash: The problem is that with lots and lots of shielding, you can't actually build anything. Either you need various fine tuned machinery working like clockwork (operated by many people) or you need to use your fingers, which tend to lose the required dexterity when clad in inches of lead. And working for days to months with your hands in direct contact with lead isn't conductive to sound health either. $\endgroup$
    – Pavel
    Aug 8, 2017 at 6:28
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    $\begingroup$ @Pavel You should be able to extract fuel from the pool with only one operator and the equipment on site. Not easily but you can and once you've got it the rest is relatively easy, provided you remembered to build the generator first. $\endgroup$
    – Ash
    Aug 8, 2017 at 11:19

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