Privacy Policy

Last updated: June 25, 2026

The Short Version

Arythm encrypts your cycle data end-to-end before it ever leaves your device. We cannot read your health information — only you and your partner can. Raw health data from Apple Health, your Apple Watch, and Oura Ring never leaves your phone.

Data We Collect

Arythm collects and stores the following on our servers:

• Your account information (name, email, authentication provider)
• Your current cycle phase label (e.g., "Period" or "Luteal") — encrypted before transmission
• Qualitative well-being indicators (e.g., "high readiness") — encrypted before transmission
• Your couple link status

We do not collect or store raw health data such as temperature readings, flow levels, symptom logs, heart rate values, HRV measurements, or sleep data.

End-to-End Encryption

Your cycle phase is encrypted on your device using AES-256-GCM encryption before it leaves your phone. Encryption keys are generated via ECDH key exchange and stored only on your device and your partner's device — never on our servers. Not even we can read your data.

Apple Health & Apple Watch (HealthKit)

Arythm requests read-only access through Apple Health to the cycle-related data you choose to share, which may include menstrual cycle data, basal body temperature, wrist temperature (from Apple Watch Series 8 or later), resting heart rate, heart rate variability, cervical mucus quality, and ovulation test results. If you use a period app such as Flo, Clue, or Natural Cycles, Arythm reads the cycle data those apps write to Apple Health.

This data is used solely to compute your current cycle phase on your device. Arythm never writes any data to Apple Health. Raw HealthKit samples never leave your device and are never transmitted to our servers or any third party.

Oura Ring Integration

You may optionally connect your Oura Ring via OAuth2 to improve phase detection accuracy. When connected:

• Arythm fetches temperature deviation, HRV, and heart rate data from the Oura API
• All biometric data is processed entirely on your device
• Only the computed cycle phase (encrypted) and qualitative indicators (encrypted) are synced to our servers
• Raw Oura data is never stored on our servers or shared with any third party
• OAuth2 tokens are stored securely in your device's Keychain
• You can disconnect your Oura Ring at any time, which revokes API access

No History Stored

We only store your current cycle state on our servers. There is no historical log of your cycle phases. When the phase changes, the previous data is overwritten.

Data Deletion

When you unlink from your partner, all shared cycle data is deleted immediately from our servers. Your partner's app will no longer show any cycle information. Encryption keys are cleared from both devices. You can also revoke Apple Health access at any time in your iPhone's Settings.

Third-Party Services

Arythm uses the following third-party services:

• Firebase (Google) — authentication, encrypted data sync, and push notifications
• Google Sign-In (Google) — optional sign-in provider
• RevenueCat — subscription management (receives only your anonymous account identifier)
• Oura API — optional ring data integration (OAuth2, user-initiated)

Arythm does not use any analytics, advertising, or tracking SDKs.

Push Notifications

Arythm may send push notifications to inform your partner of phase changes. These notifications never contain phase names or health information — only generic messages prompting the user to open the app.

Children's Privacy

Arythm is not designed for or directed at children under the age of 13. We do not knowingly collect personal information from children under 13.

Changes to This Policy

If we update this policy, changes will be reflected on this page with an updated date.

Contact

Questions about this privacy policy? Email support@arythm.app.