How to play a song/sound when the phone is in the background

How to play a song/sound when the phone is in the background

So I have a timer that can be set by the user that will will play a
song/sound the user chooses when the timer is over. This works when its in
the foreground since NSTimer is alive. Once the phone enters the
background state, NSTimer is doesn't work. So Ive been looking at possible
solutions like the UILocalNotification but that doesn't play a sound
longer 30 secs. Is there any way I can run a timer in the background that
will trigger to play the sound/song whenever it is done? Or have a method
repeatedly check while its in the background to see if the timer would be
done? Thanks for the help.