What Facebook Knows

Facebook doesn't need access to your microphone to secretly record your conversations to know you might be interested in a trip to Mexico.

But how do they know?

You talked about Mexico with your friend at their apartment on Saturday night. You haven't read about it or searched for it online.

And in spite of what people will tell you, they do not have your phone recording audio nonstop.

Facebook knows a lot about you.

Facebook Knows Where You've Been

Location is the foundation of knowing everything about you, and Facebook knows where you and your friends are much of the time.

They probably know where you are when you open any of their apps (most people have location enabled).

If you use Instagram or allow access to your photo library in WhatsApp, they know where you were and when you were there every time you took a picture. Photos have a time stamp and latitude and longitude in the metadata, and Facebook can easily extract that.

I want to emphasize that: any app that has access to your photo library can see everywhere you've ever taken a photo and when you took it.

Facebook knows most commercial websites you visit because they have a pixel on those sites. They track you even if you're logged out.

And if you have background updates turned on, they know where you are - or at least where you are not - nearly every 15 minutes even if you leave your phone in your pocket. Background updates let them update the app so it opens a little faster, but if you're on WiFi, Facebook can use that information to guess where you are.

That's Why They Are Showing You Ads for Mexico

Even if you've never interacted online, Facebook knows the people you hang out with because they see you in the same location frequently.

All it takes is for your friend to do some research on Mexico for the algorithm to guess that you might tap on some ads about it.