Justin Barkhuff
App

Interval Timer

A green field and a narrower red field, two to one, with a white ring centered on the line between them.

My wife didn’t like any of the interval timers in the App Store, so I made her one.

Interval Timer

An interval timer is a simple tool for workouts which alternate between work and rest. You work hard for a set amount of time, rest for a set amount of time, and repeat until you’re done. It’s the clock behind circuit training and high-intensity interval training, where effort is measured in seconds instead of reps. You set how long to work and how long to rest, press start, and it does the counting for you. It even beeps through the last few seconds of each interval, so you can keep your eyes on the workout instead of the screen.

Open Interval Timer
Open Dieter’s version

February 2021

Its icon: a white ring on green.

The original

The first version was simple. The whole screen changes color with each phase: slate while you get ready, green while you work, and red while you rest. A ring empties as each interval runs down. Recorded tones count down the last three seconds, mark the halfway point of each work interval, and signal the start of each new phase. You type in your work and rest times, and it remembers them for next time.

The original, before starting: 00:10 inside a white ring on dark slate, a play button, and the work and rest times, 00:40 on green and 00:20 on red. The original during work: a green screen, the ring partly emptied around 00:27, and the total so far, 00:13, below. The original during rest: a red screen with 00:12 left, and the total so far, 00:48.

October 2026

Its icon: the original’s ring, in cream on a softer green.

The rebuild

Five years later, the original was due for a refresh. The rebuild keeps the same basic design, but almost everything under the hood is new. It keeps time with the clock instead of counting seconds, so it stays accurate even when your phone goes to sleep, and it keeps the screen awake while it runs. It installs from the browser on iPhone and Android and works offline. The tones are now generated on the fly, matched to the original recordings, and they play over your music instead of stopping it.

The rebuild, before starting: 00:10 in a cream ring on charcoal, a play button, and the work and rest times on green and red. The rebuild during work: a green screen, the ring draining around 00:27, a pause button, and the total so far, 00:13. The rebuild during rest: a red screen with 00:12 left, and the total so far, 00:48. The rebuild on iPhone, with a sheet explaining how to add it to the Home Screen from the Share menu.
Open Interval Timer

October 2026

Its icon: the middle of its dial a third of the way into work, a green sector on white with the yellow hand at its edge, under glass set into a charcoal body.

Dieter’s version

A version of the timer as Dieter Rams might have designed it, and an homage to the skeuomorphic app designs of yesteryear.

Dieter’s version before starting, in light: a white clock face with a yellow hand, the work and rest times on green and orange number wheels, a yellow key, and a speaker grille. Dieter’s version during work: a green sector of the time left on the dial with the hand at its edge, the countdown, 00:27, on white wheels, and the yellow key pushed in. Dieter’s version during rest, in dark: an orange sector on a black dial, and 00:12 on charcoal wheels.
Open Dieter’s version