Now that it's (quite inexplicably) started working again on one of my boards, I've been able to at least figure out how to
test it.
- In options make sure all users and usergroups are set to trigger.
- Now log out of your board and remove all cookies from the site. There's a Firefox add-on that makes this easy - "Remove cookies for site".
- Now if you log in to one of your accounts, then log out and log in to a second account, you will trigger the detector.
You will not trigger the detector again until you remove cookies. Apparently there's a toggle built in that prevents triggering multiple times.