Online Stopwatch & Alarm Clock

A stopwatch accurate to 1/100 second with lap records, plus an alarm that rings at a clock time you set. No install — it runs in the browser and marks your fastest and slowest split as you go.

How to use

  1. Press «Start», then hit «Lap» while it runs to record a split.
  2. «Pause» stops the clock and «Resume» continues it; «Reset» clears the laps too.
  3. On the alarm tab, choose a time and press «Set alarm» to have it ring then.

Elapsed time is measured from performance.now() differences, so the clock never jumps backwards if the system time is adjusted.

The alarm rings inside the page while this tab is open — no notification permission involved. For several countdowns at once, use the multi timer instead.

FAQ

What's the difference between split and total?

«Split» is the time since the previous lap; «Total» is the time from the start up to that lap.

Does it stay accurate if the tab is in the background?

Yes. The display may refresh more slowly, but the elapsed time is computed as a difference from the start, so the numbers stay correct.

The alarm didn't ring.

Check that the tab is still open and the device isn't muted. Audio is unlocked by the tap on «Set alarm», so if you reloaded the page you need to set it again.

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