Editing 1237: QR Code

{{comic
| number    = 1237
| date      = July 12, 2013
| title     = QR Code
| image     = qr code.png
| titletext = Remember, the installer is watching the camera for the checksum it generated, so you have to scan it using your own phone.
}}

==Explanation==
{{W|QR code}}s (quick response codes) are a type of 2D {{w|barcode}} that can be scanned using any of several apps on a smartphone. This comic illustrates installation of a new application that requires the smartphone to scan a QR code on its own screen. There is no conceivable purpose for such a step, so it would be completely silly. Even with two mirrors or a front-facing camera and mirror, most smartphones would be unable to simultaneously display the camera feed for the QR scanner and the QR code itself. The only way to do it would be to take a picture of the QR code with a digital camera and then scan the screen of the camera. The "12 seconds remaining" part indicates that there is a time limit for this, and thus a ''quick response'' is necessary.

If scanned, the QR code in the comic reads <tt>http://xkcd.com/1237/scan/</tt>, a link to a nearly identical image, but the line above the QR code reads, "To continue reading," and the caption reads, "How to trap a webcomic reader in an infinite loop". The QR code is identical to the previous one. So, if scanned again, it would simply return the scanner to the same image in an "infinite loop".

In the title text, it is revealed that not only is there a time limit, but that the QR code must be scanned using the same phone that's displaying the code. Doing this using the phone's own camera is impossible. The only way to scan the code using the same phone would be by taking a screenshot and opening it with an app that scans for QR codes in images, rather than using the camera. While such apps do exist, most smartphone users would have no need for such an app and are unlikely to have one installed on an older phone, but these days both iPhone and Android phones come with a built-in QR code scanner that can scan images from the gallery.

==Transcript==
:[A smartphone. On the display, the following text:]
:"To continue installing, scan this code. 12 seconds remaining"
:[A particularly recursive QR code is displayed on the screen.]
:[Caption below the panel:]
:How to freak out a mobile app user.

{{comic discussion}}
[[Category:Smartphones]]