Online Alarm Clock

Set an alarm for any time in the next 24 hours directly in your browser, with no app, account, or download. Pick an hour and minute, press Set Alarm, and a live countdown shows exactly how long remains. If the time has already passed today, the alarm rolls over to tomorrow automatically. When it rings, snooze for five minutes or dismiss it.

How to Use

Enter the hour in 24-hour format and the minute, then press Set Alarm. The page shows the target time with a Today or Tomorrow label and starts a countdown. Use Test Sound to confirm your speakers and volume before relying on the alarm. While armed, Cancel clears it. When it rings, Snooze postpones for five minutes and Dismiss stops it completely.

How the Countdown and Rollover Work

The tool computes the next occurrence of the chosen wall-clock time. If that time is still ahead today, it targets today; if the time is equal to or earlier than the current moment, it moves the target to tomorrow. Setting 07:30 at 18:00 therefore schedules tomorrow morning, and setting 18:00 at exactly 18:00 also schedules tomorrow, because the comparison is inclusive.

The countdown ticks four times per second and formats the remaining time as HH:MM:SS, rounding up so a fraction of a second left still shows as one second. The clock and countdown use your device’s local time zone. Because the target is minute-aligned, setting 07:30 when the clock reads 07:30:20 schedules tomorrow, not a ring forty seconds from now.

Worked Scenarios

At 18:00 you set 07:30. The status reads Armed 07:30 (Tomorrow) and the countdown shows 13:30:00. At 18:00 you set 18:05. The countdown shows 00:05:00. At 06:00 you set 06:01. The countdown shows 00:01:00. If you press Snooze at 07:30:00, the next countdown starts at 00:05:00 and the status shows Armed 07:35 (Today).

What Happens When It Rings

The alarm plays a two-tone beep built with the Web Audio API: two short 880 Hz sine tones about a third of a second apart, repeated roughly every 1.2 seconds until you respond. Audio is generated locally, so the page does not download a sound file. Snooze stops the ringing and schedules a new target five minutes out. Dismiss stops the ringing and returns the page to idle. Because browser audio needs a user gesture to start, press Test Sound or Set Alarm at least once after loading the page so the audio context is unlocked.

Keep the Tab Open

This is the estate agent of limitations: location matters. The alarm only runs while the page stays open. It keeps working when the tab is in the background or the window is minimized, but closing the tab or quitting the browser ends it. Background tabs are throttled, so the ring can land a few seconds late. If the computer sleeps, no JavaScript runs and the alarm waits until the machine wakes. Treat this as a desktop backup alarm, not a substitute for your phone’s clock, and test the sound before trusting it with something important.

When a Browser Alarm Beats a Phone Alarm

A laptop alarm is convenient when your phone is charging in another room, when you are already at a desk and want a nudge five minutes before a call, or when you need a hands-free timer while cooking or working in another window. It is also handy as a Pomodoro-style cue to stand up every hour without installing a timer app. Because the page is plain and local, it works as long as the browser stays open and the machine stays awake.

Getting a Reliable Ring

Reliability comes down to a few habits. Open the tab well before the alarm is due, leave the browser running, and stop the machine from sleeping if the alarm matters. On a laptop, plug in the charger and set the power plan to stay awake; on a desktop, make sure the screen lock does not suspend the session.

Turn the system volume up, keep the tab unmuted, and press Test Sound once. The test uses the same tone and gain as the real ring, so if you can hear it, the alarm will be audible. Some operating systems route Web Audio to a different output device than you expect, so verify with the speakers or headphones you will actually be near.

Avoid stacking alarms. The page holds a single target, and pressing Set Alarm again silently replaces the current one. If you need two cues, use a second browser profile or a separate countdown timer.

Common Mistakes

Closing the tab and expecting the alarm to survive. Setting an alarm on a laptop that will sleep or shut its lid. Assuming second-level precision, when the target is minute-aligned. Leaving the system or tab muted. And setting a new time while one is already armed instead of pressing Cancel first, which silently replaces the old alarm. Trusting an alarm you have not heard once: press Test Sound before you walk away.

Related Tools

• Stopwatch & Timer
• Countdown Timer
• Pomodoro Timer
• World Clock
• Sleep Calculator