Detect what's going on a window tab

Question

Is it possible to detect the activity on an opened tab from a different website?

For example, a visitor clicked a window tab from my website to example.com, I want to detect when he presses some button inside, how is it possible?

Answer 1

This is not possible, because as mentioned above it's a huge security risk. Imagine the possibilities this would open up for invasion of privacy.

Disclaimer notwithstanding, the only way to do this would be via a browser extension/add-on or with an application running on the same computer as the browser.