I recently purchased a WikiReader. I got mine on eBay for about $20, but they're also available on Amazon.
This is one of those devices that has very little practical application. But it's the kind of thing that's absolutely amazing. I would have declared it to be impossible as recently as 20 years ago, mostly because it contains so much data in such a small package.
The WikiReader bills itself as "the Internet without the Internet". It is a small self-contained device which contains in a mini SD card (almost) the entire contents of the English-language Wikipedia. It is an electronic encylopedia with approximately three million articles on every conceivable subject. In short, it's the (somewhat imperfectly rendered) sum total of all human knowledge, in a package weighing only a few ounces, measuring four inches by four inches, and powered by two AAA batteries (included).
As I mentioned, there are few practical applications for this device. It is quite true that all of the information contained is available on the Internet. And that information is also available, in much more reliable form, in any library. But what makes this device unique is that all of that information is contained within the WikiReader's internal memory, meaning that the information is accessible even when you are miles from the nearest library, and even when Internet connectivity is unavailable for some reason.
As discussed below, the WikiReader has a few shortcomings that make it somewhat difficult to use in normal situations. However, it does seem to have two applications where its value would far outweigh it's own weight in gold.
Even though the device lacks many practical applications, the impractical applications are the reasons why I bought it. It's best to be prepared for anything, and the WikiReader would be the most valuable device known to mankind in a handful of situations. While these situations are extremely unlikely, it seems to me that the low cost and extremely high utility in those situations make it a must-have item.
While there are no documented cases in real life, science fiction is full of situations in which the protagonist is involved in some form of involuntary time travel. The most famous example is probably A Connecticut Yankee in King Arthur's Court by Mark Twain. Other prominent examples include Island in the Sea of Time by S.M. Stirling, and 1632 by Eric Flint. In all of these, the characters are forced to piece together modern knowledge imperfectly with the tools available. In fact, one of the major characters in 1632 turns out to be the 1911 Encyclopedia Britannica. And I have instructions for obtaining your own copy on my 1911 Encyclopedia Britannica page. It's another thing you should do now. Once you've been transported back in time, it will be too late--or too early, depending on how you look at it.
The chances of being involved in inadvertent time travel are admittedly quite slim. But do you really want to take any chances? Having the knowledge of the 21st Century in your pocket will make turn what would otherwise be a very unpleasant experience into one where you could quickly become a very important member of your new society.
Of course, once you travel back in time, you're quite likely to land in an era where AAA batteries are unavailable. That will not be a major problem. My AAA batteries have lasted a few weeks now, and I have little doubt that they will last the promised several months. But the WikiReader seems to have such a low current draw that almost any source of 3 volts should be more than adequate to power it. You should be able to run it using several homemade cells in series, or perhaps series-parallel. It might require some experimentation. Simply keep adding cells until the WikiReader comes to life. Of course, your first order of business after arriving in your new time should be to read up on battery chemistry, and take good notes. Then, when the AAA's finally give out, you'll have all the knowledge necessary to make new ones. When that time comes, you'll discover that you should be able to build adequate batteries during almost any time period. You'll need only two dissimilar metals and some sort of acid. Copper, zinc, and lemons will work very well, and should be available in most time periods. Again, this should be one of the first items you research upon arrival, since it will be impossible once your initial batteries die.
A closely related scenario, and probably somewhat more likely, is the possibility of a "SHTF" or "TEOTWAWKI" situation. As a result of nuclear war, disease, zombies, or perhaps some other cause, the world will be thrown back into a new dark age. All knowledge will be lost, other than what you are able to carry in your pocket. This is sometimes referred to as "The End Of the World As We Know It" (TEOTWAWKI), or sometimes, "The S*** Hits The Fan" (SHTF or TSHTF). As with time travel scenarios, the knowledge contained within your WikiReader might be what is necessary to rebuild society. You will be a valuable member of society if you are able to furnish this information. Indeed, your foresight in having the WikiReader in your "bug out bag" will render you a hero.
While the probability of a SHTF or TEOTWAWKI scenario might be low, once again, given the huge benefit and low cost, owning a WikiReader will have an incredibly favorable cost-benefit relationship.
The WikiReader is not a perfect device, and it does have some shortcomings. In fact, the shortcomings make it less useful in normal situations, although these problems will seem minor, indeed, in a SHTF or time travel situation. But let's address some of the shortcomings.
The WikiReader has an LCD screen that can be trying to read. The text is quite small. The contrast can be adjusted, but it is still somewhat difficult to read unless the light is just right. There is no backlight of any kind. The screen is the way it is for a reason, namely, to conserve battery life. If you need to find one critical fact, it's not a major hurdle. But if you want to read for hours on end, it would be extremely fatiguing.
To navigate, you do need to use the touch screen. You need to type your search term into a tiny on-screen keyboard, and then you need to click on just the right spot. Eventually, you get used to it, but it is difficult to quickly navigate. Again, this kind of criticism would be seen as trivial compared to the knowledge you would possess when sent back to the Dark Ages. But in modern times, it can get slightly annoying.
You do not get the complete version of Wikipedia. First of all, you get the text only, with no images. I suppose if you were trying to build a telegraph to impress Louis XIV, those images would give you a lot of practical guidance. The images are not there; so you'll need to rely on the text. Also, tables within Wikipedia are not included. I've heard other criticisms that formulas are not shown, but I have not found this to be true. Every article I've looked at with a formula seems to show the formula properly, and this includes complicated formulas including Greek letters, special symbols, square root signs, etc. So I don't think you'll find that many formulas are missing, although there might be a few.
I don't think this is a fair criticism. While there are undoubtedly some errors, they are actually quite rare. Read a few Wikipedia articles about subjects you know. You will amost always find a few facts about which you can nitpick. But in general, the articles are quite good, although the quality of the writing is sometimes poor. I have found that the reliability is quite good in articles about history (for example, subjects prior to 1900). Also, the treatment of science and technology is usually very good. Numerous studies show that Wikipedia compares quite favorably to other encyclopedias, such as the Encyclopedia Britannica. In fact, Wikipedia has one very great advantage over other encyclopedias, and that is its sheer size. If you have doubts as to the accuracy of any given fact, it is very likely that the given fact appears in numerous Wikipedia articles. Since you have access to all three million, it's quite possible that you'll find treatments of the subject in question in multiple articles, and you can compare the information.
They typical criticism of Wikipedia is that the articles can be changed by anyone. While that is true, it's also true that the erroneous information can also be changed back by anyone, something that is not true of traditional encyclopedias. And even if some malefactor decided to vandalize Wikipedia the day that WikiReader downloaded it, it is extremely unlikely that the vandal was able to track down every single related page. So it seems to me for the time traveler or SHTF participant, Wikipedia is actually an excellent single choice for your information needs.
Potential time travelers worry that the batteries will eventually die. As noted above, you should be able to whip up a new battery without too much difficulty. TEOTWAWKI afficionados worry that an Electromagnetic Pulse event will destory the WikiReader when you need it most. This is actually quite unlikely. If you want to learn more about the facts surrounding EMP, then you should read some of the sources cited in my EMP Bibliography. (In particular, read the four-part series of articles referenced near the top of that page.) Contrary to popular perception, EMP is unlikely to destroy small electronic devices, unless they are connected to some external "antenna" at the time of the EMP event. Since the WikiReader is such a small physical size, it's unlikely to have a sufficiently large "antenna" to be subject to a high-altitude nuclear detonation or any kind of solar phenomenon. It's certainly possible, of course. For example, if your WikiReader is sitting near a power line at that fateful moment, there might be sufficient energy transferred from the line to the device just by inductive coupling. So storing it near large metallic objects is probably a bad idea. Of course, it's also true that the WikiReader could be destroyed by physically breaking it or getting it wet. So there are no guarantees, but I think that EMP is actually a relatively minor worry.
The WikiReader is a fascinating device. I would have declared it impossible only a few years ago, but it's a reality. The fact that there are better alternatives really just illustrates how far our technology has come. There are probably a few practical applications that I haven't thought of. I'll probably take the thing camping with me, in case I want to read about some subject miles away from any internet connection. And it would perform well in a subway or other location where internet service is unavailable.
If you have an Android device, the Wikipedia Offline Reader (WikiPock) is probably a better alternative, since it is probably easier to use (although will not have the amazingly long battery life of the WikiReader. If you have a computer on which you want to use Wikipedia offline, your best bet is probably to download the entire Wikipedia database yourself.
In short, it's one of those gadgets that I'll rarely use, but when I do need it, it will be the most useful device on the planet.
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