title: Trigger an event when the user exits a geofence
body: <p>Is there a way to define a geofence (center and radius) around the current location of an iOS device, and have the system trigger a callback function in my app when the device exits the geofence? Will this mechanism can wake up a closed app?</p>
  
  <p>I would like to avoid extensive GPS usage, so I would prefer a system message over periodic GPS polling, even at the price of reduced accuracy.</p>