If your adversary is the NSA(/GRU/Mossad/etc) - you're fucked. Throw away all your electronic devices, torch your house, and hope you make it to Belize before they shut the borders to you.

If your adversary is Law Enforcement, they'll get cell tower data (quite likely without a warrant by just asking), and they'll then mislead a court and jury about how accurate that data is: https://www.newyorker.com/news/news-desk/what-your-cell-phon...

This link: http://urgentcomm.com/psap/different-strokes says that since '05 wireless carriers in The US have been required to do better than just "which cell tower you're connected to", but for some percentage of connections they're required to provide 50 or 150m location accuracy - which they can apparently do using three cell towers and triangulation. Since they're happy to hand over cell tower data to law enforcement when asked (or possibly when asked with a warrant) - I wouldn't bet against then handing this E911 Phase 2 level of location accuracy over.

Somewhat more worryingly... The cell providers seem to be happily monetising that data too: https://techcrunch.com/2017/10/15/mobile-phone-companies-app... https://www.theverge.com/2013/4/9/4187654/how-carriers-sell-...

Now out of the four big technology companies - two of them own a mobile OS and so can do whatever-the-fuck they want with your phone if you're "in their camp" and of the remaining two, one of them actually sells you stuff to make a living, the other makes their money by surveilling you.

With Facebook's warchest - what do you reckon the chances are of them _not_ buying cellphone location data on the open market to add to their advertising-marketing machine?

I'm not saying I know they are - but I do know that the data about location down to perhaps 50m accuracy or less is legally required to be available to the cell operators - and they've been caught in the past selling that data - and Facebook have _very_ deep pockets to pay for data to match against theirs. (And there is almost _zero_ chance that whatever the cell companies might to to "anonymise" that cell location data, Facebook wouldn't be able to de-anonymise it by correlating to to other data they collect.)

But yeah, having your phone use a VPN no doubt helps...