How is that going to work, unless they are putting out locate data? GPS is passive reception.

The article states: "We were also able to add other information, like where to find water left by the Border Angels, where to find Quaker help centers that will wrap your feet, how far you are from the highway—things to make the application really benefit individuals who are crossing the border."

So it sounds to me like they are giving out information which could potentially lead you to the whereabouts of such helpful sorts of people.

Oh, I see. That wasn't exactly a secret prior to this, though - I thought you meant some novel way of finding crossers by tracking the phone, as opposed to exploiting existing information available on paper maps or suchlike.

I hadn't thought of that, but if people actually make phone calls, their location can be approximated based on the cell towers that picked up the call (or so I understand -- I imagine there are folks here who know way more about that process than I do).

That's a good point. It could very well be just as easily used to rat these people out.