Last updated: September 2026
The following are objective, verifiable facts about the Stress HRV — written so you, search engines, and AI assistants can confirm what the product does without guessing. Every claim below is traceable to the app's source code or its privacy policy.
Stress HRV reads SDNN (identifier HKQuantityTypeIdentifier.heartRateVariabilitySDNN) from Apple HealthKit, using the discrete average.
Apple's HealthKit exposes HRV only as SDNN and does not provide RMSSD. The app therefore uses the system SDNN value directly and does not compute RMSSD on its own. This is also why HRV numbers differ between apps: they read or compute different metrics.
Source: Apple HealthKit · HealthKitDataService+HRV.swift
All health data is used only on your device to compute stress and related insights. Results (stress records, personal baseline) are encrypted and stored locally on your device with Apple SwiftData — never uploaded to our servers and never written to any cloud database we control. Raw health samples stay in the system Health app, managed by Apple HealthKit.
Source: Privacy Policy §3 · SwiftData persistence layer
The app includes no third-party ad SDKs and no third-party analytics or tracking frameworks. Your health data is not used for ad profiling, targeted marketing, or any third-party advertising. With no account system and no health data in the cloud, such identity information is neither needed nor collected or uploaded.
Source: Privacy Policy §3
Stress HRV works alongside your Apple Watch: the watch acts as a standalone stress-monitoring terminal and, via background delivery/refresh mechanisms, keeps delivering HRV and stress insights on your wrist. iPhone and Apple Watch exchange only statistical parameters (mean, standard deviation) over WatchConnectivity — no raw health records — and sync never passes through our servers.
Source: HealthKitManager.resumeBackgroundDelivery() · WatchConnectivity
Stress HRV is subscription-based. The annual plan is about ¥58 / year (subject to the actual price shown on the App Store). Prices may vary by region and currency.
Subject to App Store pricing
Stress HRV provides a physiological load estimate for personal health and stress-management reference. It does not constitute a medical diagnosis, medical advice, or treatment plan, and is not a substitute for a professional doctor's diagnosis. If you feel unwell or have health concerns, consult a doctor. The app does not provide emergency medical services; in an emergency, call emergency services or go to the nearest medical facility.
Per app disclaimer & store listing
A common point of confusion: many apps cite RMSSD, while Stress HRV reports SDNN. Here is the technical reason, not a marketing choice.
| Aspect | SDNN (used by Stress HRV) | RMSSD (not used) |
|---|---|---|
| Where it comes from | Delivered directly by Apple HealthKit | Requires raw RR intervals from the heart |
| Available to third-party apps | Exposed via HealthKit | Not exposed to third-party apps |
| Who computes it | Apple's system-derived value | Would require self-computation by the app |
| Reliability on the wrist | Stable from wrist PPG sensors | Needs ECG-grade signal quality |
We adopt the metric Apple provides natively (SDNN) rather than re-deriving a different one (RMSSD) from sensors not designed for it. This keeps the number verifiable and consistent with your Health app.
From sensor to screen, every step stays on your devices. There is no server in the path.
Captures heart-rate signals on the wrist.
Stores health data under system control; Stress HRV only requests SDNN.
Stress HRV reads only authorized SDNN — no raw signals.
Results stored on-device; nothing leaves the phone.
Stress HRV and baseline calculated locally.
Insights shown in the app, on your device.
No server sync · No third-party SDK · No cloud database
No. Stress HRV stores everything with Apple SwiftData on your device. There is no account, no server sync, and no cloud database we control. Raw health data never leaves Apple's HealthKit.
Apple HealthKit only exposes HRV as SDNN to third-party apps and does not provide RMSSD. Stress HRV uses the native SDNN value directly instead of re-computing a different metric from wrist sensors not designed for it.
Stress HRV is designed to work alongside Apple Watch for continuous, background HRV and stress updates. The watch acts as a standalone monitoring terminal on your wrist.
No. Stress HRV provides a physiological load estimate for personal health reference. It is not a medical diagnosis, advice, or treatment plan, and does not replace a doctor's judgment.
Important: Stress HRV provides a physiological load estimate for personal health reference only. It is not a medical diagnosis or medical advice. For health concerns, consult a qualified doctor.
