A student studying in a library leaves their laptop open with an alarm set for 3:45 PM to remind them to catch the bus home. The browser tab stays open, and when the alarm fires, the sound alerts them without needing to install any app.
A cook following a recipe sets an alarm for 20 minutes from now to check the oven. Instead of using a countdown timer, they set an absolute alarm for 7:20 PM so they can glance at the clock and know exactly when the timer will fire.
A remote worker taking a lunch break sets an alarm for 1:30 PM to return to their desk. They keep the alarm tab open in the background while browsing other sites. The notification pops up even when the tab is not actively visible.
A traveler in a hotel room sets an alarm for 6:00 AM on their laptop since their phone is charging across the room. The fullscreen mode makes the clock visible from a distance, and the alarm sound is loud enough to wake them up.
The alarm clock runs entirely in your browser. You set a target time, and the app calculates the difference between the current time and your target. It then counts down using your device's system clock, which stays accurate even if the browser throttles background tabs.
When the countdown reaches zero, the app plays an alarm sound using the Web Audio API. No audio files are downloaded. The sounds are generated programmatically by the browser, which means they work offline and load instantly.
If you allow browser notifications, the alarm will also send a system notification when it fires. This is useful if you have switched to another tab or minimized the browser. The notification appears in your operating system's notification center.
The snooze button adds 5 minutes to the alarm time and resumes the countdown. You can snooze repeatedly, though each snooze delays the alarm by the same 5-minute interval. The alarm settings are saved to your browser's local storage, so they persist if you accidentally close and reopen the tab.
Input
Current time 2:30 PM, alarm set for 3:45 PM
Output
Alarm fires in 1 hour 15 minutes
The countdown shows the exact remaining time, updating every second.
Input
Current time 11:50 PM, alarm set for 6:00 AM
Output
Alarm fires in 6 hours 10 minutes (next day)
If the target time has already passed today, the alarm automatically sets for tomorrow.
Input
Alarm fires, user clicks Snooze
Output
Alarm re-fires in 5 minutes at 6:05 AM
Each snooze adds exactly 5 minutes. The snooze counter shows how many times you have snoozed.
Pitfalls to avoid
Does the online alarm clock work when my tab is in the background?
The alarm sound plays when the tab is active or visible. For background tabs, the countdown continues accurately using the system clock, but browsers may delay audio playback until you return to the tab. Enable browser notifications to get alerted even when the tab is not visible.
Will the alarm wake me up if my computer is asleep?
No. If your computer goes to sleep or hibernates, the browser cannot play sounds. You need to keep your computer awake. Adjust your power settings to prevent sleep, or use a dedicated alarm app on your phone for wake-up alarms.
Do I need to install anything?
No. The alarm clock runs entirely in your browser. No downloads, plugins, or extensions are needed. The alarm sounds are generated by the Web Audio API, so they work without any audio files.
Can I use a 12-hour format (AM/PM)?
The alarm uses a 24-hour input for precision. To set a PM time, add 12 to the hour. For example, 2:30 PM is 14:30, and 8:00 PM is 20:00. Midnight is 00:00 and noon is 12:00.
How does the snooze button work?
Clicking snooze adds 5 minutes to the alarm time and resumes the countdown. You can snooze multiple times. Each snooze adds the same 5-minute delay. The snooze counter shows how many times you have snoozed so you know how long you have been delaying.
Is the alarm accurate?
The alarm uses your device's system clock via Date.now(), which is typically synchronized with internet time servers (NTP). The countdown stays accurate even if the browser throttles background tabs because it recalculates remaining time from the system clock on each tick.
What alarm sounds are available?
Three sounds are available: a classic beep (repeated square wave), a chime (ascending sine wave notes), and a digital ring (alternating triangle wave tones). All sounds are generated using the Web Audio API, so no downloads are needed. You can preview each sound before arming the alarm.
Can I set multiple alarms?
This alarm clock supports one active alarm at a time. If you need multiple alarms, you can open the page in multiple browser tabs and set a different time in each tab.
The alarm clock uses your device's system clock, which is typically synchronized with NTP servers. For the alarm to work, the browser tab must remain open and your computer must not go to sleep. The alarm is not a replacement for a dedicated wake-up alarm on your phone.