> I heard stories about how super advanced invasive surveillance let's people like Target know that you're pregnant before you actually know yourself. But I just don't buy it.

I believe it. But it wasn't super-advanced surveillance. It was, as I recall, 2010's "machine learning" basically drawing inferences about purchase history to determine what sorts of personalized advertisements to mail to you or print on your receipts, or whatever.

I believe it because I worked at another large American retailer similar to Target at the time and though I was not directly involved, I was aware that other departments in our company were working on similar things. It wasn't that advanced or outlandish, it was just finding trends in the huge amount of historical purchase data we had. I can absolutely believe that it was similar at Target. People who bought these things typically bought baby-related stuff 3-6 months later, so lets send them some coupons for that baby-related stuff in 2 months. It's unlikely the fact it was baby-related was actually relevant, it probably just sent coupons for whatever the predicted purchases were.

An individuals purchase history was probably correlated either by rewards program membership (preferred) or credit cards used. If you just paid cash and didn't use swipe your membership card, it was unlikely the purchase would be associated to you.