Okay, now I understand. So basically leave the GPS started until it actually is changed, then record the change, stop it, and then set my service to restart in 30 minutes.
This way it will start at 30 minutes and when it changes stop and reset the timer.
Another question then - you mentioned the Start(0,0) using the biggest amount of battery. Is there a more appropriate setting for this, that will help to reserve battery and still receive a good notification that change happened? Or should I just play with it? I'm not sure what the distance would represent - feet, meters, or miles.