How does it work?
Click the time and type a number to count down from. Press SPACE or click the Start button to go. It'll count down, go amber with three minutes left, and red when the time is up.
I'm using Safari. Why don't the keyboard shortcuts work in fullscreen mode?
It's a limitation with Safari. Switch to Chrome instead, or use the mouse cursor when fullscreen.
Can I use this at such and such conference?
Sure, help yourself. I just made it for fun.