Online Alarm Clock

Type the time you want, in either the twelve-hour or the twenty-four-hour form, and the page works out whether you mean today or tomorrow: a time that has already gone by is read as tomorrow. Give the alarm a label and it appears on the page and in the tab title, so a pinned tab tells you what it is for without being opened.

The alarm time is stored in your browser and the page reopens on it, so a reload does not lose an alarm you set an hour ago. Nothing is uploaded, there is no account and no email address is asked for. The ring time itself is compared against your device clock on every frame rather than counted down in ticks, so a tab that has been throttled in the background still rings at the right moment instead of late.

This is the part most pages leave out. An alarm clock online lives inside a browser tab, and a tab that has been closed runs nothing at all. If you close the tab, quit the browser or restart the machine, the alarm will not sound. The tab can be in the background and it can be behind other windows, but it has to exist.

The device also has to be awake. A laptop that suspends and a phone that locks and goes to sleep both stop running the page, and the alarm arrives late or not at all when the machine wakes up. A browser page cannot wake a sleeping device, and any page that tells you otherwise is describing something it does not do. If you need to be woken up, your phone alarm app is the right tool, because the operating system can wake the hardware and a web page cannot.

Sound has one more condition: browsers will not play audio on a page nobody has interacted with. Setting the alarm counts as that interaction, which is why the test sound button is there — press it once and you know the tab is allowed to make noise. A system notification can be shown as well, but only if you grant notification permission, and the page does not ask until you turn that option on.

The sound is synthesized in the browser with the Web Audio API rather than downloaded, so it starts instantly, costs no bandwidth and works with no connection once the page has loaded. Several tones are offered because one of them will be wrong in a quiet office and another will be missed in a workshop, and there is a silent option that flashes the page instead, for a room where sound is not acceptable.

When the alarm rings you can stop it or snooze it, and the readout stays on screen with the label you gave it so it is obvious which alarm went off. Presets cover the times people set most often. An alarm is the right tool when you are aiming at a clock time; when you want a fixed length of time from now, the online timer counts that down and chimes at the end, and for a date rather than a time today the countdown timer is the one to use.