Dozens of companies buy location data from mobile apps, ad networks, cell networks, wifi networks, etc. and resell it. Some of the platforms will let you geofence your store then track phones back to where they "go home" to charge that night and then mail coupons to that address.
I’m loose on the terminology but there’s a market for “offline data” correlation.
Gist of it is if your cellphone says you went wherever, there’re intuitions about what you bought. For example, stores have Bluetooth and Wi-Fi beacons on top of aisles - if your phone beacons but doesn’t connect, the store can pull a device ID (so to speak), and again correlate.
Similarly interesting is “retargeting” that tracks you’ve unsubscribed from emails and the retargets a similar ad.
The Dominik Kosorin books on adtech for a technical audience (Amazon) were illuminating and also broke my spirt on privacy. This stuff is everywhere and there’s an identity graph out there that has your life. No dodging it until regulations change or you go offline.
Edit - some other interesting angles. Third party cookie blocks in browsers harmed the industry. One of the main suggested recovery approaches is building graphs on authenticated logins. Every resource accessed post-login has a good chance of being that user. This is behind all the “sign in with Google/FB,” and known for a while as part of adtech. The primary issue with authn’d tracking is the friction of logging in, and the power it gives to closed networks that can track post-login easily like Google, FB, Apple.
What is the new, de-frictioned login flow pushed widely now as a way to go passwordless and solve the many security problems? All do-good messaging? Passkeys. What is also a de-fricituoned post-authentication user graph, if you use it to sign into everything? Passkeys. Adtech is a cancerous industry.
What's the angle on this?