An interval timer repeats a work period and a rest period for a set number of rounds. The usual starter is 40 seconds on, 20 seconds off, eight rounds, which is a four minute circuit you can survive. Change the three numbers for Tabata (20 and 10), for lifting rests, or for a class station rotation. The choice is stored in the URL.
Each phase gets its own alarm so you do not have to watch the digits during a burpee. The label on the clock says whether you are in work or rest, and which round you are on. Space starts and pauses the current phase. Reset takes you back to round one.
For a single hold, a 30 second timer or a 45 second timer is simpler. Use this page when the rest is part of the workout and you do not want to reset by hand. Fullscreen is worth it in a gym or a living room where you will be on the floor. Pick a beep you can hear over music, and allow notifications only if the device is somewhere you will see it.
Questions
What is a good first interval?
40 seconds of work, 20 seconds of rest, and 8 rounds. Adjust after one circuit, not before.
Can I share a workout?
Yes. Work, rest, and rounds are query parameters on this page, so the link opens the same circuit.
Does it alarm on every interval?
Yes. Each switch from work to rest, and from rest to work, plays the sound you picked.