Cero - Interval Timer for HIIT

What It Does

Cero is a powerful interval timer designed specifically for high-intensity interval training (HIIT), Tabata, circuit training, boxing rounds, and hybrid race preparation like HYROX. The app provides a flexible framework for building custom workout sessions with advanced interval programming, heart rate monitoring, and seamless integration across iPhone and Apple Watch.

Who It's For

Cero is built for athletes, fitness enthusiasts, and trainers who need precise interval timing for structured workouts. Whether you're doing HIIT runs, strength and conditioning circuits, indoor cycling intervals, or boxing rounds, Cero keeps you focused on performance rather than managing the clock.

Key Features & Capabilities

• Flexible Session Builder: Create quick work/rest timers or program detailed workouts with custom intervals, colors, icons, and intensity levels. Configure work periods, recovery times, sets, warm-ups, and cool-downs to match your training style.
• Adaptive Heart Rate Training: Extend recovery intervals until you reach your target heart rate, then guide hard efforts with low and high HR alerts. Pair Bluetooth heart-rate monitors with iPhone or use Apple Watch heart-rate data.
• Apple Ecosystem Integration: Run workouts from your wrist with the redesigned Apple Watch app, follow sessions with Live Activities and Dynamic Island, start timers from Home Screen widgets, and control workouts with Siri and Shortcuts.
• Gym Display Mode: Project your workout on a larger screen or mirrored TV for group training or better visibility.
• Workout History & Recaps: Review completed sessions with detailed recaps showing time, intervals, estimated calories, and heart rate data. Share your recap as an image or export history as PDF/CSV.
• Music Integration: Choose a default song or assign specific music to individual intervals to maintain motivation throughout your session.
• Countdown & Stopwatch Tools: Built-in countdown timer and lap stopwatch for warm-ups, station changes, rest periods, and race-day practice.

What Makes It Different

Cero stands out with its adaptive heart rate feature that intelligently adjusts recovery periods based on your actual physiological state, ensuring optimal training intensity. The app's deep integration with Apple's ecosystem—including Live Activities, widgets, Shortcuts, and comprehensive Apple Watch functionality—provides unmatched convenience. Automatic iCloud backups protect your custom timers, and the ability to share workouts via file or QR code makes it easy to distribute training plans to clients or training partners.

With customizable sounds, voice cues, vibrations, and background alerts, Cero adapts to your training environment whether you're in the gym, outdoors, or training at home.