Online Alarm Clock | Set an Alarm in Your Browser

Set the time, leave the tab open, and the page counts down to it and sounds. The tone is generated by the browser's audio engine rather than loaded as a file, so there is nothing to download and it works with the connection off. If the time has already gone today, the alarm rolls over to tomorrow rather than firing at once.

Two things get in the way of any alarm in a browser, and both are worth knowing before you rely on one. A browser will not play sound until you have interacted with the page, which is why the alarm is armed by a button rather than by the clock alone. And a laptop that goes to sleep stops running the page, so an alarm across a lunch break needs the machine kept awake. Closing the tab ends it altogether, because no page can wake a device it is no longer running on, so for an alarm that has to survive a locked screen use the clock app on your phone.

For a length of time rather than a time of day, the countdown timer counts down to a date and the stopwatch counts up. To see what time it is somewhere else before setting this, the world clock has the offsets.

How to use it

Pick the time you want the alarm to go off.
Press Set, and the countdown and the target time appear.
Leave the tab open. Press Stop when the alarm rings.

Questions

Will the alarm work if I close the tab?

No. The countdown lives in the page; closing the tab or quitting the browser ends it. Leave the tab open, and on a laptop, stop it from sleeping.

Why is there no sound?

Browsers block audio until you interact with the page. Pressing Set counts as that interaction, so use the button rather than reloading into a pre-set alarm. Also check the tab is not muted.

Does it work offline?

Yes, once the page has loaded. The clock reads your device's time and the tone is synthesised locally, so no network is needed.

Will it ring if the tab is in the background?

Usually yes, as long as the browser is still running and the machine is awake. Background tabs are throttled, which can make the countdown display update less often, but the alarm is scheduled rather than counted down to, so it still fires at the right moment.

Why does it ask me to press a button first?

Because browsers refuse to play sound on a page nobody has interacted with, which is the rule that stops websites shouting at you. Arming the alarm is that interaction, and it also means the page can check the audio engine works before you are relying on it.

Will it work if my computer sleeps?

No, and no web page can. A sleeping machine is not running the browser. For anything longer than a short break, set the alarm on a phone as well, or turn off sleep in your power settings for as long as you need it.

Can I use it as a reminder while I work?

That is what it is for. Keep it in a pinned tab, set the time, and carry on. Nothing is stored, so closing the tab loses the alarm, which is deliberate: an alarm you forgot you set is worse than no alarm.

Your data stays on your device

Everything above runs inside your browser as WebAssembly compiled from Rust. Nothing you type is uploaded, logged or stored on a server. You can load this page once, go offline, and it still works.

This page makes no requests at all, to anywhere. That is not a promise in the copy: it is a Content-Security-Policy header your browser enforces, and connect-src on it is none. Open the network tab and watch nothing happen.