The homebrew scene has always been a clever bunch of developers, but the new app Keep WiFi Alive by XDA user winphoneviet has to be the most ingenious creation we've seen yet. Yes, they've figured out a method to keep your WiFi on, even if you lock your phone for twelve hours. Unlike some of the other system level hacks though, Keep WiFi Alive actually doesn't require any funny business -- no interop unlock and no rooted privileges (just a dev unlock). In fact, any developer could probably do this using the Marketplace-approved Mango APIs. We'll let winphoneviet explain how it all works in their own words:
Idea for this app:
Ok, for all of you who interested in this app, I give you the idea.
Basically, if you use a lot radio and music apps, you can notice that if you stream the music online using WIFI, it will keep the WIFI alive even you lock the screen, you can try by turning off the data connection then use WIFI only.
From this idea, I write an app with Background Audio that try to stream the music from the mp3 file (from somewhere in the internet) over WIFI, the mp3 can be "blank" (no sound) and repeat playing the file
The important thing is, if you pause the streaming, after a few minutes (i don't know exactly), the OS will "kill" the Background Audio task, then it will turn off the WIFI again.
In a nutshell, the app is streaming a blank music file in order to keep the Background task awake which is exactly how music apps like 8tracks or iHeartRadio work. In this case, you can't hear anything and the file is in a constant loop so your Wi-Fi is connected at all times. We tried it on our Nokia Lumia 900 and it works like a charm, though you can hear a very faint hiss if you have headphones on.
There are a few asterisks to go along with this method, however. For one, if you pause the blank audio file or play something else from the Music+Videos Hub the background task will eventually be killed off and your Wi-Fi will go back to its regular behavior. Also, because your phone is constantly streaming something from the web it could have a significant effect on battery life, so make sure you use it in doses.
If you have a dev-unlocked device, feel free to pick up the XAP file by visiting the XDA-Developers Forum thread.
Via: Plaffo (Translated)
Source: XDA-Developers Forum