Alarm clock online

These alarms ring while this tab stays open, and only then: the browser gives a page no way to ring in the background, so a closed tab is a silent alarm. Tones are synthesized in the tab with the Web Audio API, so nothing needs to download; browsers let sound start only after you interact with the page, and adding or testing an alarm counts as that interaction. Snoozing runs on the device clock, and the alarm list lives in this tab's memory only: leaving the page clears it. Nothing leaves the tab.