HIIT Interval Timer | Cero

Build an interval workout around the way you train.

Cero is a flexible interval timer for HIIT, Tabata, circuit training, WODs and HYROX preparation. Set up a quick work/rest timer or program each interval in detail. Distinct colors, large controls and reliable cues keep you focused on the session instead of the clock.

BUILD YOUR SESSION
• Set work, recovery, sets, warm-up and cool-down.
• Create advanced workouts with custom intervals, colors, icons and intensity levels.
• Save, duplicate and reorder timers.
• Share timers by file or QR code.
• Review completed sessions in workout history.

STAY IN THE WORKOUT
• Follow compatible sessions with Live Activities and Dynamic Island.
• Start saved or recent timers from Home Screen widgets.
• Use Siri and Shortcuts to start, pause, resume and stop a timer.
• Put Gym Display on a larger screen or mirrored TV.
• Choose a default song or assign music to individual intervals.
• Customize sounds, voice cues, vibrations and background alerts.

TRAIN BY HEART RATE
Adaptive HR can extend recovery until you reach your target heart rate, then guide hard efforts with low and high alerts. Pair a Bluetooth heart-rate monitor with iPhone or train with heart-rate data from Apple Watch.

COUNTDOWN AND STOPWATCH
The built-in countdown and lap stopwatch cover warm-ups, station changes, rest periods and race-day practice. Stopwatch sessions continue after you close and reopen the app.

ON APPLE WATCH
Run saved workouts from your wrist, follow heart rate and use the standalone countdown and stopwatch.

Cero can save completed workouts and estimated calories to Apple Health. Automatic iCloud backups help protect saved timers and custom intervals.

Useful for HIIT, Tabata, circuits, EMOM-style workouts, boxing rounds, strength and conditioning, indoor cycling, running intervals and hybrid race preparation.

Feedback and suggestions: hi@flawless.studio

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