Does the alarm work if I close the tab?

No. Because everything runs locally in the page, the tab must stay open and the device awake for the alarm to sound. There is no server pushing a notification.

Where does the alarm sound come from?

The tone is synthesised in your browser with the Web Audio API. No audio file is downloaded and nothing is sent to any server.

Is my alarm time stored anywhere?

No. The time and label stay in the page only and are never uploaded or saved to a server.

Online Alarm Clock

Set an alarm in your browser — the tone is generated locally, no app needed.

A simple online alarm clock

Set a wake-up time or a quick reminder right in your browser. Choose the time, add an optional label, and the clock rings with a tone generated locally — no app to install and no audio file to download.

Keep the tab open and the device awake; everything runs in the page, so nothing about your alarm ever leaves your device.