iPhone and iOS 4’s persistent wifi

Updated 19/05/2011

There’s not a lot of information surrounding the new persistent wifi feature in iOS 4 and how it affects iPhones. I did some experimentation and managed to find something which i’d like to share with those who are seeking the same information.

First of all on iPod Touches, persistent wifi works as advertised and stays on wether or not the phone is plugged into the charger. This is so it can maintain a constant data connection for Push Notifications and mail checking.

Now for iPhones. Prior to iOS 4.3, persistent wifi worked albeit conditionally and under the following conditions:

  • 3G is unavailable
  • Cellular data is turned off
  • iPhone is plugged into charger

But post 4.3, persistent wifi will ONLY work under the following condition:

  • iPhone is plugged into charger

This situation may or may not change in the future but I will update this post when I have more info.

10 thoughts on “iPhone and iOS 4’s persistent wifi”

  1. Do you Know if this behavior has changed with iOS 4.3 and up? My wi-fi gets dropped after 15 seconds when my iphone 4 (ios 4.3, 4.3.1 and 4.3.2) goes to sleep. Cellular data and 3G is off. After wakeup the connection is reastablished after 5-10 seconds, strong signal, stays until sleep and is then lost again and so on. With the same device and configuration and ios 4.2.1 (before upgrade to 4.3) it was like you descibed here. I tried to restore the firmware with DFU but no success but i cant find much others with this problem and apple support gives different answers to this question every time i ask. 

    1. You are completely right. I ran a few tests and on 4.3.2 after turning off cellular data and/or 3G, WiFi disconnects after 35 – 40 seconds.
      I’ll run the same test on my iPod Touch and let you know how I go. Perhaps it’s different for those devices.

      1. Ok I can confirm that WiFi stays on persistently for the iPod Touch and works as advertised. It does not disconnect like on the iPhone. Looks like they changed the behaviour with 4.3. I’ll update the article.

  2. Thank you for your time. I am not the only one – yeah! So, i hope apple will change that back because persistent wi-fi is not realy wireless if you need to hang on a power source (normaly with a wire) 😉

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  5. Hi, I have the iPhone 4s – how do I test if the wireless is cutting off when it goes to sleep (and is unplugged)? Pretty sure it’s not, because my Cellular Usage is low, but I’d love to confirm.

    1. Hi Stephanie,

      If you leave it for say half an hour then unlock it, you can tell if wifi has disconnected or not by looking at the wifi/3g indicator. If it quickly switches from 3G to wifi, you’ll know it’s disconnected.
      Hope this helps.

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