Has anybody done any work on creating alarms based on GPS location? I'm doing some planning on features for my app, MaeCalTasks.

One thought I had was to create tasks and add GPS coordinates to a set of tasks (say shopping lists). Each time the user gets within a certain range of the stores tagged via lat/long in the tasks, I would create an Alarm that would go off to tell the user not to forget to stop at the next closest store.

Any thoughts?