How to determine user interests?

Question

Browsers

Suppose a user visits my site and I know the user's mobile phone number.
How can user interests be determined?
Google determines them...
Reading: When a user visits Google sites such as YouTube and our partners, Google stores an advertising preference cookie in their browser. It allows you to determine the type of content viewed. Based on this information, ads are selected that match the user's interests and demographics.

Answer 1

At the snap of a finger, nothing. It is a huge and complex system for assembling and storing information.

Answer 2

In general, no way, large banner networks, metrics scripts, and others can collect such statistics by collecting information about which user visits which sites with which urls (for example, he went to an online store on a page about a dildo, with a referrer of a certain forum - here you already have preferences appeared - visits the forum, looking for dildos).
They won’t give this information to anyone for free, and they won’t give it away for money, but pay a percentage of the goods sold - yes (this fact will also be information about the user).
ps you can find out what kind of hardware the user has, approximately by the user agent of the video card and, if necessary, the simplest benchmark (you can also ask for information about the camera), and there, at the price of the hardware, you can make some assumptions about solvency and commitment to one of the pc / mac camps.

Answer 3

Google defines them...

Do you feel strong to compete with Google? This is a huge complex information collection system distributed over zillions of sites. Some do not like it (here I am for example) and try to cheat ... in general, most do not care about it ...
But I don’t think that you will have enough resources - it’s easier to ask Google itself :)