Smartphones know so much about us. Why not sell that data?

Once, only hairdressers and bartenders knew people’s secrets.

Now, smartphones know everything — where people go, what they search for, what they buy, what they do for fun and when they go to bed. That is why advertisers, and tech companies like Google and Facebook, are finding new, sophisticated ways to track people on their phones and reach them with individualized, hypertargeted ads. And they are doing it without cookies, those tiny bits of code that follow users around the Internet, because cookies don’t work on mobile devices.