[shadowmore]

I considered this, but opted for a physical visual timer where the amount of time you set it to is covered by a red overlay on the clock face, which recedes until it reaches zero.

That way you get not only the benefit of the alarm at the end, but also a visually distinct display of how much time is left if you ever look over at the timer while it's counting down.

May be more useful to me than most because of ADHD and the time blindness that comes with it, but either way, it's been a great help and a way to avoid paying attention to my phone while working.