Effective date: July 30, 2026
SteadyHeartBeat is an iOS app published by Halfmarble LLC (“halfmarble”, “we”, “us”). This policy explains how SteadyHeartBeat handles your information.
The short version: your health data never leaves your iPhone. There are no accounts, no sign-in, no analytics, no advertising, and no third-party tracking — and halfmarble never receives your data.
None. SteadyHeartBeat does not collect, transmit, or share any personal data, and it does not track you across other apps or websites. There is no advertising identifier (IDFA) and no attribution. All computation — zone calculation, heart-rate analysis, histogram generation — happens on your device; halfmarble does not operate a server that receives personal health data.
SteadyHeartBeat reads health data through Apple’s HealthKit framework, with your permission. None of it ever leaves your iPhone through SteadyHeartBeat.
| Data type | Source | Purpose |
|---|---|---|
| Heart rate (live) | AirPods with heart-rate monitoring | Real-time voice readout and chart display during a workout |
| Respiratory rate (live) | AirPods with heart-rate monitoring | Displayed during a workout as breaths/min |
| Active calories burned | HealthKit (calculated from HR) | Displayed during a workout; saved to your workout session |
| Date of birth | Your Health profile | Calculates your personal heart-rate zones (Tanaka formula: maxHR = 208 − 0.7 × age) |
| Resting heart rate | Apple Watch (background) | Pre-workout screen, cardiovascular baseline indicator |
| Heart rate variability (HRV) | Apple Watch (background) | Pre-workout screen, autonomic health indicator |
| Cardio fitness (VO₂ max) | Apple Watch (background) | Pre-workout screen, fitness context indicator |
| Biological sex | Your Health profile | Selects age- and sex-based reference ranges for cardio fitness |
| Body mass (weight) | Your Health profile | Estimates the energy cost of elevation gain during a workout |
| Step count | HealthKit (during workout) | Shown during and after the workout |
| Walking + running distance | HealthKit (during workout) | Shown during and after the workout |
| Flights climbed | HealthKit (during workout) | Shown during and after the workout |
When you complete a monitoring session, SteadyHeartBeat saves a workout record to Apple Health by default — duration, activity type (boxing, cycling, running, walking, hiking, or other), heart rate, and active calories — so it counts toward your Apple Fitness rings. That record is governed by Apple’s Health privacy settings and your own iCloud Health sync settings. You can turn this off in the app under Preferences → Apple Health → Save workouts to Apple Health; with it off, the workout is discarded and never written to Apple Health.
Completed session summaries — HR timeline, zone distribution, and histogram — and your on-device profile (age, biological sex, any self-reported conditions, and manually entered metrics) are saved to the app’s private storage on your iPhone. This storage is explicitly excluded from iCloud and iTunes backups, so it stays on your device, and it is removed when you delete the app.
Keeping your data on-device must not lock you out of it. Preferences → Your Data gives you two unconditional actions — no account, no request form, no waiting.
Export My Data assembles everything the app stores — your workout sessions and on-device profile — into a complete, readable copy and hands it to the iOS share sheet. Where it goes is your choice; the app uploads nothing. The export sheet also offers Anonymize for Research…, which produces a de-identified copy (random identifiers; identity and absolute timestamps removed) for you to donate to a research effort of your own choosing. halfmarble receives nothing in either case. (Where halfmarble itself runs opt-in research, it never takes individual records — only differential-privacy-protected aggregates; see our data policy.)
Delete All Data immediately erases every session and the on-device profile. Workout records you already saved to Apple Health remain in Health, under your control there.
SteadyHeartBeat contains no third-party SDKs — no analytics, advertising, crash-reporting, or social frameworks. No third-party partners receive any data from the app. This website (halfmarble.com) likewise uses no analytics or tracking of any kind and sets no cookies.
SteadyHeartBeat is not directed at children under 13 years of age, and we do not knowingly collect personal information from children under 13.
We may update this policy from time to time. Any material change will be posted on this page with a new effective date.
Questions about this policy? Email privacy@halfmarble.com.
For data deletion: use Delete All Data in the app (Preferences → Your Data), or simply delete the app from your iPhone. For Apple Health data, use the Health app’s data-management features.
SteadyHeartBeat is built under halfmarble’s Glass Box principle: all algorithmic logic is deterministic, traceable to peer-reviewed science, and runs locally on your device. The full data philosophy is at halfmarble.com/glass-box/data.html.