Set the alarm clock for 4:51 am

Leave this tab open — the alarm only rings while the tab stays open.

The alarm goes off in: ::

You can also try the other alarm clocks

Alarm clock for 4:49 am Alarm clock for 4:50 am Alarm clock for 4:52 am Alarm clock for 4:53 am

Going to bed for a 4:51 am alarm

Asleep by 7:36 pm — 6 full sleep cycles, about 9 hours
Asleep by 9:06 pm — 5 full sleep cycles, about 7 hours
Asleep by 10:36 pm — 4 full sleep cycles, about 6 hours

A sleep cycle runs about 90 minutes, and most people take around 15 minutes to drop off. Waking at the end of a cycle feels easier than waking in the middle of one.

4:51 am across the country

London	4:51 am
Birmingham	4:51 am
Manchester	4:51 am
Glasgow	4:51 am
Belfast	4:51 am

Times are worked out live in your browser, so daylight saving is already accounted for.

How to use the online alarm clock

Preparing early for a shift at a London fire station leaves room to check your uniform, boots and journey before you need to leave. An alarm set for 4:51 am can mark the point when those final preparations should begin, while 5:00 am remains an easy reference time if you are working backwards from departure.

A firefighter relying on this alarm needs the signal to remain available until it sounds. Check that the selected tone is audible and that the device will not go to sleep during the wait. If the browser page is closed or the device sleeps before 4:51 am, no sound will play and the shift could begin without you. Keeping the device connected to power may also prevent an overnight battery warning from interfering with the alarm.

While laying out kit in the darkness, a bright screen can feel harsh against the low light of the room. Lower brightness before setting the alarm, then place the display face down or angle it away from the bed while leaving the device awake. At this hour of the night, that reduces unnecessary glare when you check the time and lets the room stay dim until your 4:51 am signal sounds.

Common questions

Will it still be right when the clocks change?

Yes. It reads your device's local clock, so the move between GMT and BST at the end of March and October is picked up automatically, as long as the computer's date, time and time zone are set correctly.

Can I use this on a phone?

It works in a mobile browser, but phones lock the screen and suspend background tabs far more readily than a laptop does, which can stop the alarm sounding. For anything important, a desktop or a plugged-in laptop is the steadier option.

Does the alarm still work if I close the tab?

No. Everything runs inside this page, so closing the tab — or quitting the browser altogether — ends the countdown there and then. Leaving it open in the background is all it asks, and switching to another tab makes no difference.

What happens if my laptop goes to sleep before 4:51 am?

The tab sleeps along with it and the alarm will not sound on time, if at all. If you are relying on it, change the power settings so the machine stays awake, or keep a phone alarm running as well.