About waking at 12:00 PM
Midday alarms are almost always reminders — a lunch break you would otherwise work through, a call, or a dose. If you are using one to interrupt a working stretch, put it somewhere you have to stand up to silence it.
Leave the tab open
A browser alarm can only ring while its page is open. It does not have to be the tab you are looking at, and on a desktop it does not have to be the window in front — but closing the tab or quitting the browser stops it. For anything you genuinely cannot miss, set a second alarm on your phone as a backup. That is true of every browser-based alarm clock, not just this one.