Online alarm clock
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Thursday 1 October 2026, UK time (BST)
No alarm set
Choose a time and press Set alarm.
How to use it
- Type the time you want to be alerted, in UK time and the 24-hour clock (07:30, 14:00).
- Pick a sound and press Test sound to check your volume.
- Press Set alarm, or tap a quick button for an alarm in 10, 20 or 30 minutes or an hour.
- When it rings, press Stop alarm, or Snooze 5 min for five more minutes.
Keyboard: Space sets or stops the alarm and R cancels it. Your last time and sound are saved on this device.
What you need to know first
A browser alarm is not as dependable as the alarm app on your phone. It only rings if:
- this tab stays open (it can be in the background);
- the computer or phone does not go to sleep, and the lid stays open on a laptop;
- the volume is up and the tab is not muted.
While an alarm is set, supported browsers keep the screen awake, which helps. On iPhones and iPads, Safari pauses sound when you switch apps or lock the screen, so leave the page open in front. For waking up in the morning or anything you can't afford to miss, use your phone's built-in alarm as well.
How the alarm time is worked out
If the time you enter is still to come today, the alarm is set for today. If it has already passed, it is set for the same time tomorrow. The time is UK time (Europe/London), so a UK clock change overnight is handled for you.
Worked example: at 10:15pm on Thursday 1 October, an alarm for 07:00 is set for Friday 2 October at 07:00, and the page tells you it rings in 8 hours 45 minutes. The sound is scheduled in the browser's audio clock the moment you press Set alarm, so it plays on time even when the tab is in the background.
Choosing a sound
Beeps are two alternating tones, like a kitchen timer. Chime is softer, for a reminder in a quiet office. Buzzer is a low, harsh tone that is hard to sleep through. Each plays for one minute, then stops. The flashing clock and the tab title also show that the alarm has gone off.
Sharing an alarm time
Add ?at= and a 24-hour time to the address, for example datetime.uk/alarm-clock/?at=07:30. The page opens with the time filled in. Browsers only allow sound after a click, so you still press Set alarm to switch it on.
Related tools
To be alerted after a length of time rather than at a time of day, use the online timer or the 20-minute timer for a power nap. To see the time in other countries, open the world clock.
Frequently asked questions
Will the alarm go off if my computer goes to sleep?
No. A sleeping computer or phone stops the browser, so the alarm can't ring. Change your power settings so the device stays awake, or use your phone's built-in alarm.
Does the alarm work in a background tab?
Yes. The alarm sound is scheduled when you press Set alarm, so it plays on time while you use other tabs or apps on a computer. The tab itself must stay open.
What time zone does the alarm use?
UK time, which is GMT in winter and BST in summer. If you are outside the UK, enter the UK time you want, or check the difference on the world clock first.
How long does the alarm ring for?
One minute, unless you stop it or snooze it first. The numbers also flash and the tab title changes, so you can see it has gone off.
Can I set more than one alarm?
One alarm at a time. Press Cancel alarm before you set a different time. For a second alarm, open the page in another tab.