Does the 20 second timer keep running if I switch tabs?

Yes. It counts against the real clock, so switching tabs or returning after a browser pause shows the correct remaining time. Keep the tab open for the finish sound and notification.

How do I start the 20 second timer?

It loads ready to go — just press Start (or the spacebar). It will play the selected sound when time is up and can show a notification if notifications are allowed.

20 Second Timer — online, fullscreen, no ads

About the 20 second timer

This page loads a ready-to-go 20 second timer. Press start and it counts down with big, clear digits, then alerts you with a sound and a notification. Use fullscreen for a classroom or across the room. No ads, no sign-up, and offline support after the page has been cached.

Questions

Does the 20 second timer keep running if I switch tabs?: Yes. It counts against the real clock, so switching tabs or returning after a browser pause shows the correct remaining time. Keep the tab open for the finish sound and notification.
How do I start the 20 second timer?: It loads ready to go — just press Start (or the spacebar). It will play the selected sound when time is up and can show a notification if notifications are allowed.