title: Detecting active use of camera
body: <p>I need to detect whenever another app is using the iPhone's/iPad's camera while my app is running. My app keeps on running in background (audio), but it does not use the camera itself. I just need to find out if another app is using any camera at all.</p>
  
  <p>Moreover, I want to use as little CPU resources as possible to minimize battery usage.</p>
  
  <p>I've tried without success:</p>
  
  <ul>
  <li>running a simple <code>AVCaptureSession</code> to catch interruption notifications (it's never notified)</li>
  <li>call <code>lockForConfiguration</code> on all <code>AVCaptureDevice</code>s</li>
  <li>periodically monitor the <code>enabled</code> property of <code>AVCaptureInputPort</code> (it's always YES)</li>
  <li>periodically monitor the <code>connected</code> property of <code>AVCaptureDevice</code> (it's always YES)</li>
  </ul>
  
  <p>For clarification:</p>
  
  <ul>
  <li>I do not need a way to detect existence of camera(s)</li>
  <li>I do not need a way to find out if the camera is active in my app</li>
  </ul>
  
  <p>Thanks for any pointers.</p>
  
  <p>EDIT: this a security feature: I want to warn the user if there's a slight possibility that a malicious (foreground) app is taking a photo or video of the user or the surroundings while my app is in active (background) use.</p>