title: Android count down timer in background
body: <p>I have an Android app with manage a countdowntimer (class CountDownTimer) that it is shown in app screen, to show how much time left to arrive 00:00.</p>
  
  <p>My problem now is that when I press home button or when I launch another app the app/timer does not run in the background. So I suspect I must do a service, but how? Colleagues have said to me that I must do something special for when the device gets locked in order for the timer to continue. I want to wake up when arrived to 0.</p>
  
  <p>What is the best way to do this?</p>