title: Core Bluetooth scan for peripherals while the phone's screen is off
body: <p>I need to keep scanning for broadcasts from peripherals while the app is in background and when the phone's screen is off. Scanning from background was successful but I can't scan (can't trigger didDiscoverPeripheral) broadcasts when the phone' screen is off. </p>
  
  <p>So far I've implemented <code>beginBackgroundTaskWithExpirationHandler</code> inside <code>applicationDidEnterBackground</code> and that's how I am able to scan in background. So how should I do this?</p>