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On the iPhone "Cellular" settings screen, you can choose which apps are allowed to use cellular data and which can only communicate over wi-fi. In iOS 9, Apple introduced Wi-Fi Assist which automatically switches to cellular data when a wi-fi connection is present, but not functioning well. Can anyone confirm that the iPhone will respect the cellular data use settings when in wi-fi assist mode?

Example scenario:

  1. In the settings, I specify that Tinder isn't allowed to use cellular data.
  2. I am browsing Tinder on wi-fi
  3. The wi-fi connection becomes unreliable and Wi-Fi Assist kicks in
  4. Will my phone now use cellular data for Tinder, since it's pretending that it's still on wi-fi? Or will it apply the cellular data rules and not use Wi-Fi Assist with this specific app?
  • Great question! – Timothy Mueller-Harder Oct 26 '15 at 5:14
  • A possibly helpful page which does not answer your question: support.apple.com/en-us/HT205296 – Timothy Mueller-Harder Oct 26 '15 at 5:22
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    And I can half-answer it right now: iOS will not let any app for which you have cellular data turned off use cellular data. I don't know whether it will stay on the poor Wi-Fi signal or complain that you aren't connected to the Internet, but you don't need to worry about it using data. – Timothy Mueller-Harder Oct 26 '15 at 5:26
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I have tested this with my own app and home server (plus my horrid internet at one part of my house). I created an application that sends an HTTP request to the server when you press a button and an application on my server that makes a sound when it receives it and records the IP address.

When the app was allowed to use cellular data, it went through quickly and had an external IP (confirming the request went through cellular). When it was not allowed to use cellular data, it tried to use Wi-Fi and eventually did send the request (after some time), using a local IP address.

So Wi-Fi assist does respect the rules that you have set in your phone's settings.

  • Great detective work, thanks! One question: when it was trying and failing to use wifi for your app, did you verify that it was using WI fi assist (I.e., cellular) for other apps that were allowed to use it? – octern Nov 8 '15 at 16:42
  • I tested the iTunes Store and it worked very quickly. After making the post I did more testing to verify where the request was coming from. I setup my server to also record the IP address. My server was on the inside of my house and port forwarded. When the request came from Wi-Fi assist (cellular) it had an external IP (confirming cellular was used), and when cellular was turned off for that application, the request had a local IP. – AppleBetas Nov 8 '15 at 19:01
  • Excellent, thank you! Incidentally, your user icon didn't stand out to me before, but now that I'm reading this on my phone it's making my brain hurt (: – octern Nov 8 '15 at 19:30
  • No problem, and *evil laugh* :) – AppleBetas Nov 8 '15 at 19:43

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