Slog: Zone 2 Cardio

Heart rate, color, hands-free

Free · Designed for iPhone. Not verified for macOS.

Just say "Hey Siri, Start Zone 2." Wrist turns green when you're in zone, blue when low, red when high. Glance, don't squint at heart rate. Free. No account. Slog — Zone 2 cardio you can glance at, not squint at. Just say "Hey Siri, Start Zone 2." A workout begins. Your wrist turns green when you're in Zone 2, blue when your heart rate is too low, red when it's too high. That's the entire app. No reading numbers mid-stride. HOW IT WORKS 1. Voice start. No tapping, no menus. Say "Hey Siri, Start Zone 2" from across the room. 2. Glance for color. Full-screen color tells you what to do — speed up, slow down, or hold steady. No squinting at a heart-rate number while running. 3. End when you're done. Workouts save to Apple Health and count toward your Fitness rings. WHY ZONE 2 Zone 2 is sustained aerobic work at 60–70 percent of your max heart rate — what exercise physiologists call conversational pace. It's the foundation of cardiovascular fitness, supported by decades of research and recommended by the American Heart Association. The catch: it's hard to stay in Zone 2 without a tool. Most apps bury heart rate behind charts and zones 1 through 5. Slog shows you one thing — are you in Zone 2 or not — and gets out of the way. WHAT'S IN (THE WHOLE APP) — Voice-activated workout via "Hey Siri, Start Zone 2" — Full-screen color UI: green, blue, red, gray — Heart rate displayed as a fallback number — Elapsed time — Auto-calculated Zone 2 from your age in Apple Health, or set manually — Workouts saved to Apple Health and Apple Fitness rings — Watch face complication for one-tap launch — Haptic taps when you cross zone boundaries ON YOUR IPHONE Your phone is the treadmill console. During a watch workout, Slog on iPhone mirrors your heart rate live — a big number, a full-screen color, and your elapsed time, readable from feet away. Afterwards, History shows every session with time in Zone 2 and your weekly minutes against the 150-minute aerobic target. Set your range once in Zones (age-based, or Karvonen if you know your resting heart rate) and sync it to your watch with one tap. WHAT'S NOT IN (INTENTIONALLY) No multi-zone display. No splits, no intervals, no audio cues, no Strava bridge, no chest-strap pairing. Saying no is the product. PRIVACY Heart rate stays on your device. There's no account, no servers, no analytics, no tracking. Slog reads from Apple HealthKit and writes your workouts back to it. That's it. PRICING Free.

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The developer, William Cai, indicated that the app’s privacy practices may include handling of data as described below. For more information, see the developer’s privacy policy .

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    Information

    Seller
    William Cai
    Size
    3 MB
    Category
    Health & Fitness
    Compatibility
    Requires iOS 26.4 or later.
    • iPhone
      Requires iOS 26.4 or later.
    • Mac
      Requires macOS 26.4 or later and a Mac with Apple M1 chip or later.
    • Apple Vision
      Requires visionOS 26.4 or later.
    • Apple Watch
      Requires watchOS 10.0 or later.
    Languages
    English
    Age Rating
    4+
    Copyright
    © 2026 William Cai
  • Developer Website
  • Privacy Policy

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