[zarzavat]

I assume it’s tied to logging in or using the account while logged in. Email is a separate system, it’s possible they linked up the email system to the accounts system, but the easiest way to implement this would just be to update a timestamp every time someone logs in or makes an authenticated browser request.

[mcny]

Welp, back to Firefox containers it is then.

For those who don't know, you can have multiple Google sessions in different Firefox containers in a single Firefox profile/window.

This is an official Firefox adding as far as I know. It works with Firefox sync for me (not enabled by default).

https://addons.mozilla.org/en-US/firefox/addon/multi-account...

[dataflow]

> but the easiest way to implement this would just be to update a timestamp every time someone logs in

You don't have to speculate here. They clearly say "Activity might include these actions you take when you sign in or while you’re signed: Reading or sending an email, Using Google Search, etc."

So it's not just "did they log in".