How do sites detect whether someone is running adblocker?

I've been interested in this functionality (when a site detects your adblocker and kindly asks u to whitelist).

The only idea that comes to mind is setting a div in the layout with "ad" class or something similar, and then if a user has adblocker the adblocker would be removing this div from the dom. I don't think this would consistently work for every (or at least most of the popular) adblockers out there.