A GPS tracker becomes useless if it can't see any satellites; having worked with GPS before and seeing how effective even a thin layer of metal can attenuate the signal significantly, I'm curious as to how they were able to make this work. It seems highly unlikely that someone smuggling a tusk would leave it in clear view of the sky.
The full story details some of the tech. It was pretty well thought out. IIRC, the device communicated periodically via sat phone and would cache geodata so that if the sat phone ping failed, it could transmit previous location.
Iridium device locations can also be requested from the network based on what satellite/beam communicated through which is "accurate to within 10Km 80% of the time"
