Main character Joe gets transported from the modern age into medieval times. In Joe's pocket is his smartphone and a solar charger to keep it powered indefinitely. The internet and GPS are gone and unfortunately Joe didn't download a local copy of Wikipedia, maps, or anything unusually prepper/survivalist like that. What common smartphone applications would people or governments find the most valuable? Photos? Video? Calculator? Music? Flashlight? Addictive casual games? Fart sounds? What medieval technology or process would be most enhanced with a smartphone's basic capabilities?

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    $\begingroup$ You'll have a hard struggle getting this (albeit fun) question not closed as opinion based. $\endgroup$
    – Guran
    Commented Jun 21, 2017 at 8:28
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    $\begingroup$ Cat pictures duuh! On a more serious note: I am not sure if you can just say "common smartphone applications". Are you only interested in the ones you listed, or would you for example prefer to use a list of pre-installed apps on the currently most popular smartphones? You mentioned games, which makes my previous point a bit complicated, as they are normally not pre-installed and therefore answers could be based around their specific assumptions as to what is "common". And I take we should ignore the "he will be burned as a witch at the stake for catching our souls in a mystical box"-trope? $\endgroup$
    – Secespitus
    Commented Jun 21, 2017 at 8:31
  • $\begingroup$ One irreproducible smart phone won't do much during the few years of its life. You may want to reformulate the question and let Joe be transported to 14th century Paris or Rome with a his truck carrying a shipment of one thousand smart phones and solar chargers. $\endgroup$
    – AlexP
    Commented Jun 21, 2017 at 8:38
  • $\begingroup$ @AleP a whole truck for a measly 1000 smartphones? What shipping company can compete while leaving so much empty space? $\endgroup$
    – dot_Sp0T
    Commented Jun 21, 2017 at 9:00
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    $\begingroup$ @AlexP taking an iPhone as reference, 1000 smartphones will take ~1 m^3 (that is 90cm by 145cm by 80cm going with the measures found here), 1000 solar chargers (going for the Voltaic Amp @ 140cm by 40cm by 165cm, as recommended by The Independent) make a second m^3 - You can fit that in a city car! $\endgroup$
    – dot_Sp0T
    Commented Jun 21, 2017 at 10:02

4 Answers 4


Your Joe arrives in a middle age location, where the normal approach toward stranger is usually suspicious. Then your Joe takes out of his pocket (willingly or upon inspection) a black flat stone, which seems to be able to

  • generate light with nothing burning in it
  • produce sounds or even music with no musical instruments nor musicians in it
  • reproduce images of the surrounding with no painter in it
  • talk and answer question when asked (depending on the model) with nobody in it

when Joe does something on it with his fingers. This is clearly a devilish device and its bearer, Joe, is worth a quick trip to the closest Inquisition tribunal to be burnt to death or even lynched on spot.

Based on this premise, the most useful functions of the smartphone are

  • mute
  • lock screen
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    $\begingroup$ Witch burning is much more an Early Modern phenomenon that a Medieval one. In the actual Middle Ages an execution by burning at the stake was a rare event to be remembered across centuries. But anyway +1 for the common sense approach. $\endgroup$
    – AlexP
    Commented Jun 21, 2017 at 8:45
  • $\begingroup$ dayum, this is a very logical approach to the question; makes the question seem like a trick question, LOL $\endgroup$
    – Kevin fu
    Commented Jun 21, 2017 at 8:47
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    $\begingroup$ "Any sufficiently advanced technology is indistinguishable from witchcraft" sounds plausible, but the question Would relatively primitive people really confuse technology with magic? suggests otherwise. $\endgroup$
    – Golden Cuy
    Commented Jun 21, 2017 at 10:41

You'll need to be really careful before you get hung as a demon/wizard wielding a magical weapon...

  • having a camera, and being able to record and take videos/photos is invaluable as a tool to gather intel/entertainment
  • Flash light
  • as an accurate time keeping device (clock, timer)
  • you can have a "bard in a hand" with the music player (even a simple ringtone would do)
  • for taking and jotting down notes (no need for ink)
  • having a chess game installed, with AI difficulty set to impossible will trigger a bunch of chess grandmasters of the time
  • and there's A LOT more you can do, depending on the apps you have installed

But the main problem still remains: just don't get killed for being a heretic/demon/wizard/other-worldly being, or get the lords of the land searching for you and your mobile phone.

I advise against selling/trading your phone away, it would make "joe" a regular peasant.

TL;DR; Basically any function a phone has in the modern world, minus the GPS/internet, times 10.

  • $\begingroup$ I like this answer because I feel it is answering the intention of the OP. He hasn't reacted to my comment asking about clarification whether the "he will be burned as a witch at the stake for catching our souls in a mystical box"-trope should be ignored, but as he never mentioned it I feel like he wasn't going for such an approach. +1 from me for actually answering how to use different aspects of a smartphone $\endgroup$
    – Secespitus
    Commented Jun 21, 2017 at 9:10
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    $\begingroup$ The chess thing is a superb idea. The bard in hand on the other side sounds like an easy way to have someone a) punch you in the face and then b) smash your smart phone. I wish I could do that every time. $\endgroup$
    – Raditz_35
    Commented Jun 21, 2017 at 9:22

The main thing that Joe would find useful would be buzzfeed and it's "100 things that would kill you in medieval times because you are not vaccinated against them. The 101 is stench".

But if you rule this out what would be most useful is the calculator. And it's preinstalled.
Just look at your screens and see how many mathematic things were discovered after the medieval times (even the late ones).

Also - JOE HAS A FRIGGIN LOGARITHMICS MACHINE! Count the ship out of everything. Artillery angles, powder power, wall thickness, pumps litres per minute, cubic metres of materials needed for anything.
Instead of guessing and making trials by errors - count. Count and give proper measurements and force push those motherlovers into industrial produced things.

  • $\begingroup$ + for logarithms - they were a big deal back then $\endgroup$
    – glyphin
    Commented Jun 21, 2017 at 17:06

Most useful as a trade object if it doesn't get taken off him or get him burnt for witchcraft first.

Apart from that the most useful thing on it is the torch.

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    $\begingroup$ Can you flesh out a bit on how to make a trade object out of it? Nobody would trade for something which he perceives of no value. $\endgroup$
    – L.Dutch
    Commented Jun 21, 2017 at 9:37
  • $\begingroup$ @L.Dutch use your own imagination, anything unusual is a potential trade object. $\endgroup$
    – Kilisi
    Commented Jun 21, 2017 at 10:24
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    $\begingroup$ I am farmer. My donkey helps me in carrying the grains to the mill. What does your stone do for me if I give you my donkey? $\endgroup$
    – L.Dutch
    Commented Jun 21, 2017 at 12:49
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    $\begingroup$ I am a wealthy noble. I have hundreds of horses that I ride around when I'm bored. Your stone makes music! You can have a dozen horses so that I can listen to music while I ride one of my other of hundreds of horses. $\endgroup$
    – Michael
    Commented Jun 21, 2017 at 14:36
  • $\begingroup$ @L.Dutch obviously it's a luxury item, your example is silly. $\endgroup$
    – Kilisi
    Commented Jun 21, 2017 at 20:30

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