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According to the docs, calling WatchKit's sendMessage on an Apple Watch app extension wakes up the corresponding iPhone app in the background. This enables the iPhone app to provide the Watch app with data it needs, even if the iPhone app is currently not in the foreground. Unfortunatelly, I cannot find much information about this process. I'd like to know the answer to these questions: Is there a special launchOptions key present when the iPhone app starts up in the background? According to these docs, an empty launchOptions indicates that the user started the app from the home screen - all other startup reasons have their own launchOptions key. However, when testing the wakeup, I get an empty launchOptions. Are there other options that can be used to detect that the iPhone app runs in the background? For example, I expected [UIScreen mainScreen] to be nil because in the background we do not have screens and windows, but there seems to be no difference in mainScreen in the background process. Are there any limits to the background process? For example, is there a limit in how long it can run? Is there a way I can debug such a background process in XCode? Can I tell XCode "wait until the app runs on the iPhone", such that the debugger gets attached as soon as the app runs?