I\'ve tried several techniques to capture a screenshot of an app from within that app. None of the techniques appear to capture the status bar -- it ends up being black.
As an alternative solution, perhaps you could detect the connection type, similar to: https://developer.apple.com/library/ios/#samplecode/Reachability/Introduction/Intro.html . With some additional checking for the device type, you could then warn the user only in the case where they need to act.