Slog

Support

Slog does one thing: tells you whether you're in Zone 2 by changing the screen color. Below are the questions that come up most often.

Quick start

1. Install Slog on your iPhone (it goes straight to your paired Apple Watch).
2. Open the app once. Grant Health access when prompted.
3. From then on: just say "Hey Siri, Start Zone 2" to begin a workout.

How does Slog calculate my Zone 2 range?

By default: 60–70% of your max heart rate, where max HR is 220 minus your age (pulled from Apple Health). This formula has a known accuracy range of ±10–12 BPM. If you've done a lab test or know your true max from experience, override it manually in Settings.

What do the colors mean?

• Green — you're in Zone 2. Hold this pace.
• Blue — heart rate is below Zone 2. Speed up.
• Red — heart rate is above Zone 2. Slow down.
• Gray — no heart rate signal yet.

Does Slog save my workouts?

Yes. When you end a workout, it's saved to Apple Health as a Mixed Cardio workout. This counts toward your daily Exercise ring in Apple Fitness. If you have Apple Health → Strava sync enabled, it'll propagate there too.

Why doesn't Slog have [feature]?

Slog intentionally does one thing. By design, it has no workout history browser inside the app (use Apple Health), no multi-zone display, no interval builder, no splits, no audio cues, no chest-strap pairing UI, no subscription. If you want a feature-rich Zone 2 tracker, Z2 (Zone 2: Heart Rate Training) and Zones for Training are good options. Slog exists for people who want the opposite.

My Siri command isn't working

Make sure the Slog app has been opened at least once on your watch, Siri is enabled, and you're saying the exact phrase: "Hey Siri, Start Zone 2". If it still doesn't work, restart your watch.

Does Slog work without my iPhone nearby?

Yes. Slog is a standalone watchOS app. As long as your watch has access to your heart rate, it works fully without your iPhone.

Bug reports / feature requests

Email iamwillcai@gmail.com. I read everything. Include your Apple Watch model, watchOS version, and a description of what happened.

Privacy Policy

Slog stores nothing about you. There's no account, no server, no analytics, no tracking. Your heart rate and workouts live on your Apple Watch and in Apple Health. That's it.

Last updated: April 29, 2026

What Slog reads from Apple Health

With your permission:

• Heart rate — to show you whether you're in Zone 2 during a workout
• Date of birth — used once to calculate your default Zone 2 range. You can also set this manually in Settings.

You can revoke either permission any time in iPhone Settings → Health → Data Access & Devices → Slog.

What Slog writes to Apple Health

With your permission, when you finish a workout it's saved as a Mixed Cardio workout so it shows up in your Apple Fitness rings.

What Slog stores on your watch

Standard local preferences (UserDefaults): your custom Zone 2 floor and ceiling if you set them manually, and your age if you set it manually. These never leave your watch.

What Slog does NOT do

• No accounts. There is no sign-up or sign-in.
• No servers. Slog does not communicate with any backend.
• No analytics. We do not log app opens, taps, crashes, or anything else.
• No advertising. There are no ads.
• No third parties. Heart rate and workout data are never shared, sold, or transmitted to anyone.
• No tracking across apps or websites.

HealthKit — Apple's rules

Per Apple's developer terms, Slog will never use HealthKit data for advertising or marketing, sell HealthKit data, disclose HealthKit data to third parties for any purpose, or store HealthKit data in iCloud or any external service.

Children

Slog is not directed at children under 13. We do not knowingly collect any data from anyone, but especially not from children.

Changes to this policy

If this policy changes, we'll update the "Last updated" date above. Material changes will be noted in the app's update release notes.

Contact

Questions about privacy? Email iamwillcai@gmail.com.