Countdown Timer with Alarm - Presets, Sound and Tab Title Alert
Set hours, minutes and seconds, or tap a preset from 1 minute to 1 hour, and press Start.
Maintained by Hirantha Sandaruwan Lakshan. Updated 15 October 2026.
About this tool
A ring shows how much time is left, the browser tab shows the countdown in its title, and when time is up you get a short alarm and the title flashes Time is up. You can mute the sound, and you can turn on a pop-up notification if you want one. Anything from one second to 99 hours, 59 minutes and 59 seconds works, and nothing leaves your device.
How it works
The timer stores the moment it will end, not a count of seconds left. Each time it checks the clock, the time left is that end moment minus now. This keeps it correct in a background tab: Chrome can check the chained timers of a tab that has been hidden for more than five minutes, and silent for 30 seconds, only once a minute (Chrome for Developers, checked 2026-10-15), but the end moment does not change, so the next check shows the right time. Pausing keeps the time left, and resuming sets a new end moment that far ahead. A part second counts as a whole one, as on a kitchen timer, so the display reaches 00:00:00 when the time is up.
The alarm is made in the browser with the Web Audio API, with no audio file. Browsers only let a page start sound after you have interacted with it (MDN autoplay guide, checked 2026-10-15), so the page prepares the audio when you press Start. The alarm is also scheduled on the audio clock ahead of time, which is meant to keep it on time if the timers of a hidden tab run late; that is best effort and varies by browser. If the browser blocks sound, or you turn the Sound switch off, the tab title and the message on the page still tell you.
While the timer runs, the tab title shows the time left, for example 00:04:59 - Countdown timer. When the time is up it flashes Time is up! until you come back to the tab or do anything on the page, and it returns to normal when you dismiss or reset the timer. Notifications stay off until you click Enable notifications; the browser then asks permission, and the answer is granted, denied, or not decided yet (MDN, checked 2026-10-15). If you have denied them, the page explains that you must allow them in the browser settings. A notification is only shown when the page is in another tab, and it is made on your device without any server.
The longest timer is 99:59:59, which is 359,999 seconds. You can type more than 59 in the minutes or seconds box, and 90 minutes is read as 1 hour 30 minutes. Blank boxes count as zero, only whole numbers are accepted, and a timer set to zero cannot be started. The time comes from your device's clock, so changing that clock while the timer runs would change the time left.
Worked examples
Pausing and resuming
A 25 minute timer started at 14:00:00 ends at 14:25:00. If you pause at 14:10:00 with 15:00 left and resume at 14:30:00, the new end moment is 14:45:00.
Typing a length instead of using a preset
Typing 90 in the minutes box with 0 hours sets 01:30:00. The 1 hour preset sets 01:00:00 and the 15 min preset sets 00:15:00.
The longest timer
99 hours 59 minutes 59 seconds is 99 x 3,600 + 59 x 60 + 59 = 359,999 seconds, which is 4 days 3 hours 59 minutes 59 seconds. One more second is refused with a message.
Frequently asked questions
Will the timer still go off if I switch to another tab?
Yes. It works from a stored end moment, so the time left is right whenever the page checks the clock. The alarm is also scheduled on the audio clock, which is meant to keep it from being held up by a hidden tab, but that varies by browser. In Chrome the tab title and a notification can be up to a minute late in a tab that has been hidden for a long time.
Why do I need to press Start before I can hear the alarm?
Browsers block sound on a page until you have interacted with it, to stop pages playing audio by surprise. Pressing Start counts as that interaction, so the page can sound the alarm later without another click.
How do I turn the sound off?
Turn off the Sound when time is up switch. The tab title and the message on the page still show that the time is up.
How do notifications work, and what if I blocked them?
Click Enable notifications and your browser asks for permission. If you allow it, you get a pop-up when the time is up and the page is in another tab. If you blocked notifications for this site earlier, the browser will not ask again: allow them for this site in the browser's settings.
What is the longest timer I can set?
99 hours, 59 minutes and 59 seconds, which is 359,999 seconds. A timer set to zero cannot be started.
What happens if my computer sleeps while the timer runs?
The timer is based on the clock, so when the device wakes it shows the correct time left, or finishes at once if the end has passed. A sleeping device cannot sound an alarm, so the alarm comes when it wakes.
Is anything saved or sent?
No. The lengths you type, your choices and the timer stay in the page. Nothing is stored or sent, and the alarm sound is generated on your device.
Sources & references
Updated Oct 15, 2026