20 Minute Timer
Set for 20 minutes. Press start — it rings when the time is up.
This timer runs while the tab is open. If you need it to go off when your phone is in your pocket — that part needs the app.
20-20-20: the rule for screens and eyes
Optometrists have a rule of thumb for screen work: every twenty minutes, look at something twenty feet away for twenty seconds. The point is not the exact numbers — it is that the muscle focusing your eyes has been holding one position for a long time, and holding any position for a long time is what makes it ache.
The awkward part is remembering. Eye strain builds slowly and you notice it hours later, by which time the twenty-second break would have had to happen sixty times. This is precisely the kind of thing a timer is for: it remembers a small, dull, easily-skipped action that pays off only when it is repeated.
Twenty minutes is also a workable unit for the work itself — long enough to get somewhere, short enough that stopping does not feel like abandoning anything.