Set the alarm clock for 4:21 am

 

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

The alarm goes off in: ::
 
 

Going to bed for a 4:21 am alarm

  • Asleep by 7:06 pm — 6 full sleep cycles, about 9 hours
  • Asleep by 8:36 pm — 5 full sleep cycles, about 7 hours
  • Asleep by 10:06 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.

4:21 am across the country

Sydney4:21 am
Brisbane4:21 am
Adelaide3:51 am
Perth2:21 am
Darwin3:51 am

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

Online alarm clock for 4:21 am

While preparing for an astrophotography session deep in the Australian outback, set the 4:21 am alarm before packing the last batteries, lenses and warm layers. That gives you a clear cue for the planned setup rather than another time to remember in the dark. It also leaves a useful stretch before 5:00 am for reaching the chosen spot, checking the tripod and allowing your eyes to adjust.

Your early photography plan can fail quietly if the phone is still set to silent, so confirm that browser audio is audible and choose a sensible volume before settling down. A quick sound check now is more useful than discovering the setting beside the camera. Because this alarm relies on an active browser, closing it or letting the phone sleep means the 4:21 am astrophotography cue will be missed; keep the browser running and use a separate alarm if waking on time is critical.

Once the gear is ready, avoid turning the remaining night into extra preparation. Put clothes, water and a dim red torch together, then return to bed with the route already decided. The sleep left before 4:21 am will be less disturbed if there is no need to rehearse every step mentally, and a simple written checklist can hold any last details until the alarm sounds.

Common questions

Do I need to create an account or download anything?

No, there's nothing to sign up for and nothing to install. Pick a time and a sound, press Start, and it runs entirely in this browser tab.

Can I change the alarm sound?

Yes, there's a short list of tones to choose from before you press Start. Pick whichever one you're most likely to actually hear — softer sounds are easier to sleep through than a firm chime or bell.

What happens once the alarm goes off?

It rings through your device's speakers on a loop until you stop it from this page. There's no separate app notification, so make sure your volume is turned up before you rely on it.

Is this alarm accurate across daylight saving time?

It uses your device's local clock, so as long as your computer's time and date settings are correct, it'll adjust automatically when daylight saving time starts or ends.