[ry_ry]

That is auto-triggered by software detection at a device level isn't it?

[pbhjpbhj]

I tried spoofing GPS with Niantic's Ingress game, just about the second time I played, and the spoofing apps relied on the fake location flag in the dev settings - of course Niantic checked to see if that was set and refuse to work if it was [until the system was rebooted, with the flag disabled, AFAICT]. Haven't tried with PoGo as I'm more interested in playing it [with my kids, honest!] than working out how it works.

[therein]

Not necessarily. At least on Android, it is rather simple to just use Xposed Framework to basically "mock syscalls".

[BryantD]

No clear answer to this as far as anyone can tell. From the evidence it definitely looks like there's a server component, though.