title: How would iOS reminder functionality be implemented?
body: <p>What is the recommended way to implement a reminder functionality, which would survive the app being in an inactive state, and would wake it up at a predetermined time?</p>
  
  <p>Using <code>NSTimer</code> seems to be OK in the foreground, but the user should be able to set a reminder, close the app, and do something else.</p>
  
  <p>How is this done?</p>