From Twitter:
I'm back from a week at my mom's house and now I'm getting ads for her toothpaste brand, the brand I've been putting in my mouth for a week. We never talked about this brand or googled it or anything like that.
As a privacy tech worker, let me explain why this is happening.
First of all, your social media apps are not listening to you. This is a conspiracy theory. It's been debunked over and over again.
But frankly they don't need to because everything else you give them unthinkingly is way cheaper and way more powerful.
Your apps collect a ton of data from your phone. Your unique device ID. Your location. Your demographics.
Data aggregators pay to pull in data from EVERYWHERE. When I use my discount card at the grocery store? Every purchase? That's a dataset for sale.
They can match my Harris Teeter purchases to my Twitter account because I gave both those companies my email address and phone number and I agreed to all that data-sharing when I accepted those terms of service and the privacy policy.
Here's where it gets truly nuts, though.
If my phone is regularly in the same GPS location as another phone, they take note of that. They start reconstructing the web of people I'm in regular contact with.
The advertisers can cross-reference my interests and browsing history and purchase history to those around me. It starts showing ME different ads based on the people AROUND me.
Family. Friends. Coworkers.
It will serve me ads for things I DON'T WANT, but it knows someone I'm in regular contact with might want.
So. They know my mom's toothpaste. They know I was at my mom's. They know my Twitter. Now I get Twitter ads for mom's toothpaste.
Your data isn't just about you. It's about how it can be used against every person you know, and people you don't. To shape behavior unconsciously.
To subliminally get me to start a conversation about, I don't know, [bleep] toothpaste.
It never needed to listen to me for this. It's just comparing aggregated metadata.
The other thing is, this is just out there in the open. Tons of people report on this. It's just, nobody cares. We have decided our privacy just isn't worth it. It's a losing battle. We've already given away too much of ourselves.
Apple's latest updates let you block apps' tracking and Facebook is MAD. They're BEGGING you to just press accept and go back to business as usual.
Block the [bleep] out of every app's ads. It's not just about you: your data reshapes the internet.
Also an interesting read on tracking you on your cell phone
https://www.nytimes.com/interactive/2019/12/19/opinion/location-tracking-cell-phone.html 
