Wasn't there news a few years back that Android Phones uploaded location history happening while "offline" when they finally connected to WiFi; that ended up blamed as "a bug"? OTOH law enforcement has a direct access to baseband modem anyway, so they can triangulate switched off phones with batteries inside, and if those phones have large enough capacitors, even with removed batteries. Having some competent aggregator like Google might be helpful though.
IIRC there was some discussion about it on some Neo900-related forums, but it was a few years I'd looked over there. One of the reasons they had switches for both baseband modem and mic to be sure they aren't powered.
