When Hall disappeared in 1994, cell phone triangulation and other technologies commonly used in missing person cases today weren't available.

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Dark Reading covered a talk at SOURCE on tracking GSM cell phones using a variety of public data, cell tower triangulation, and voicemail hacking techniques.

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Apparently, the service makes use of cell-tower triangulation, and not GPS, to determine the users location, making it somewhat less accurate but far more widely available.

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The triangulation itself, measuring the distance between the endpoint and the three nearest cell towers, can be done by either the phone or the cloud.

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