> potential for being more insidious and more passive. Im thinking of sound beacons

I have some bad news for you - what you describe as a dystopian future hellscape was up and running by 2015. If you want to so much as slow it down, stick to F-Droid or ditch your smartphone.

[0] https://www.wired.com/2016/11/block-ultrasonic-signals-didnt...

[1] https://arstechnica.com/tech-policy/2015/11/beware-of-ads-th...

[2] https://arstechnica.com/information-technology/2017/05/there...