title: run a thread behind activities in android
body: <p>Im developing for an android aplication and I need to run a thread in the background that is going to be check the current gps and show an activity depending of the current location data but the application have diferents activities, and I need this thread running all the time no matter if I change between an activity and other.
  Can I do that ?
  I know that I can add threads to an activity but I dont know how have a main thread in the background</p>