Twenty minutes is the beat behind the 20-20-20 rule for screen fatigue: every twenty minutes, look at something about twenty feet away for twenty seconds to rest your eyes. A single beep marks each twenty-minute mark, so the break happens on its own while you stay in the work.
It doubles as an unobtrusive focus check — long enough to settle into a task, short enough to catch yourself drifting — and as a gentle pacing beat for a lab, studio, or workshop. Six reminders cover two hours as set; raise the rounds in the editor to run it across a longer stretch.
A calmer quarter-hour beat — a beep every 15 minutes, on repeat, to stretch, sip, or check in at a desk or in class. Free in your browser, no sign-up.
The half-hour is the interval ergonomics advice points to for breaking up sitting — a beep every 30 minutes, on repeat, to stand, stretch, or rest your eyes. No account, no install.