This 21 second timer is easy and simple online countdown timer clock with alarm. So it is actually 21 second countdown.
Just press start the "start" button and this twenty one second timer will start. If you want to pause the timer, no problem, just press the "pause" button and if you want to continue, press the "resume" button. When timer comes to zero minutes, zero seconds and zero milliseconds, alarm will start ringing. Press the "stop" button and alarm will stop. If you want to start again and set timer for 21 seconds or set alarm for 21 seconds, just press the "reset" button. In "timer settings" you can change the time for timer.
You may try also other countdown timers.