It's a free browser alarm — here's exactly what it can and can't do.
The alarm runs entirely in your browser. It checks your device's clock every second and plays a sound when an alarm time is reached. So it can only ring while the alarm is open and running — either the alarm page in an open tab, or its floating Show on top window. If you close the tab, close the floating window, fully quit the browser, or your device powers off, the alarm cannot ring.
It does not send push notifications and does not run in the background. There's no server and nothing is scheduled remotely — leave the clock (or its floating window) open for it to sound.
In full screen the clock requests a screen wake lock so your phone won't auto-sleep and drop the view. If you manually lock the screen, the browser may exit full screen and the alarm stops until you reopen it.
Alarms are saved in this browser on this device only (local storage). They aren't synced or sent anywhere, and clearing your browser's site data removes them. You can share a link that pre-loads a set of alarms.
On Chrome and Edge, Show on top opens an always-on-top floating window (Picture-in-Picture) that stays visible over other tabs and apps — it must stay open to ring. Firefox and Safari don't support this yet.