> IIRC only triggering the "audible ring" leaves a trace on the phone (a notification + the obvious sound), to check if someone used FMP for tracking one has to dive deep into the Google Activity Logs.

Not true, a notification is shown whenever the device is located.

Though if someone can "sneak a 2nd Google Account" onto your phone they can probably install something more nefarious and less observable.

Yeah, if someone hacks my phone/account, then they will have access to my location. If that happens them having my location ranks pretty low on my list of concerns.

The recommendation that you could disable GPS is pointless because if they could sneak a 2nd account on it they can also re-enable GPS.

Cell phone companies have your location regardless of whether or not GPS is enabled. You don't even need a smart phone.

We are talking the cell providers here, disabling GPS only slows down the initial positioning as LTE has a number of alternative ways to determine your location. That is required in places like the US were its mandated by law (E911 IIRC) that the providers are capable of providing your location to government services in real time (like 911).

So, the fact that the providers are keeping tabs on you and storing all that metadata for some government agency (cause you might be dangerous!), just means that they have discovered a way to recoup some of the investment costs. Thank your government, because the phone companies likely wouldn't have been this creative by themselves.