Set the alarm clock for 3:59 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 3:57 am Alarm clock for 3:58 am

Going to bed for a 3:59 am alarm

Asleep by 6:44 pm — 6 full sleep cycles, about 9 hours
Asleep by 8:14 pm — 5 full sleep cycles, about 7 hours
Asleep by 9:44 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.

3:59 am across the country

London	3:59 am
Birmingham	3:59 am
Manchester	3:59 am
Glasgow	3:59 am
Belfast	3:59 am

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

How to use the online alarm clock

As you finish getting ready and head out for a shift at a London fire station, an alarm for 3:59 am gives you a final prompt to pick up your keys and leave. It falls just before 4:00 am, so there is no spare stretch of time to begin another job around the house. Everything needed for the journey should already be by the door.

Your fire-station departure depends on the alarm sounding while the browser remains active and the phone or computer stays awake; if either stops running beforehand, there may be no alert at 3:59 am. A sensible check is to keep the alarm visible, leave the sound turned up and connect the device to power if its battery is low. A separate phone alarm can provide backup for a shift that cannot wait.

Stepping into London’s night air at this hour can mean meeting damp pavements, mist or lingering moisture even when rain has stopped. Keeping a light waterproof layer beside your work bag avoids searching for one after the alarm sounds. If the air outside feels close, a zipped outer layer that can be loosened during the journey is more practical than adding several heavy layers before leaving.

Common questions

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 3:59 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.

Do I need an account or an app?

Neither. Choose a time and a sound, press Start, and it runs in this browser tab. Nothing is downloaded, nothing is registered, and closing the page leaves nothing behind on the device.

Can I change the sound?

Yes, there is a short list of tones to pick from before you press Start. Softer sounds are easy to sleep through, so a firmer bell tends to be the safer choice for anything early in the morning.