Updated October 16, 2026

Privacy policy

Cernidia helps you understand personal health signals and use them in daily life. Your insights are calculated on your devices. If you connect WHOOP, the app also uses WHOOP's online services and an authorization service operated by us.

This policy covers the Cernidia app on iPhone and Apple Watch and this website. Apple Health, WHOOP, Calendar and check-ins are optional. You do not need a Cernidia account. We do not sell your data or include advertising or cross-app tracking. Cernidia contains no product analytics; see section 9a. TestFlight's separate data processing is described below.

1. Controller and contact

Sven Krain
Tiergartenstrasse 121, 30559 Hannover, Germany
cernidia@gmx.de

Sven Krain provides Cernidia as a free personal hobby project. Cernidia is the name of the app.

You can use this contact to ask about Cernidia's processing and exercise your data protection rights.

2. App data and purposes

Cernidia processes information you enter, such as energy and stress check-ins, context notes, manually recorded workouts, tasks, routines, goals, daily boundaries and preferences. It also processes generated plans, completion records and derived personal comparison values. These data are stored locally to interpret signals and provide guidance about sleep, recovery, movement and focus, together with suitable planning suggestions.

Health data and personal insights are not sent to an external AI service or used for advertising. Cernidia does not diagnose conditions or recommend treatment. Missing data stays unknown. Personal comparisons require enough readable history from a consistently identified source; a missing or changed source can leave a comparison unavailable. Insights and suggestions are calculated automatically; the app does not make solely automated decisions with legal or similarly significant effects within the meaning of GDPR Article 22.

3. Apple Health

With your permission, the iPhone app reads the data you select and that are available through Apple Health (HealthKit). These may include sleep duration and stages, heart rate, resting heart rate, heart rate variability, walking heart rate and heart rate recovery, steps, walking and running distance, flights climbed, active energy, exercise and standing time, workouts, respiratory rate, blood oxygen, wrist temperature, time in daylight and estimated cardiorespiratory fitness.

Raw samples are processed in memory for analysis; Cernidia does not keep its own persistent copy of these raw HealthKit samples. It stores limited summaries, historical estimates and comparison values. During a workout you explicitly start on Apple Watch, the app may process heart rate and save the completed workout to Apple Health with the relevant HealthKit permission.

To keep comparisons between compatible sources, these summaries can contain a locally calculated source key derived from the source app identifier and device product or model information. Cernidia does not use a raw Health sample identifier or a person identifier for this key. It does not identify a unique physical device, is not used for tracking and is not sent to the WHOOP authorization service. The key remains part of the local health summaries; hashing it does not make those summaries anonymous.

If the WHOOP app shares records with Apple Health, Cernidia can read those records under the same HealthKit permission. This does not require a direct WHOOP connection in Cernidia and includes only records WHOOP actually shares with Apple Health.

4. Direct WHOOP connection

You can choose to connect your WHOOP account. You sign in and grant access through WHOOP in the system browser. Cernidia does not receive your WHOOP password. The connection permits reading recovery, sleep, cycle and workout records and renewing access without another sign-in. We do not request access to your WHOOP profile name, email address or body measurements.

Depending on availability and your authorization, Cernidia processes data provided by WHOOP including:

• Recovery: Recovery score, resting heart rate, RMSSD heart rate variability, blood oxygen and skin temperature.
• Sleep: start and end times, naps, time in bed and awake, sleep stages, respiratory rate, sleep performance, consistency and efficiency.
• Physiological cycles and workouts: time periods, sport, Strain, average and maximum heart rate, energy expenditure and available distance and step values.
• Record matching and freshness: technical WHOOP user and record identifiers, timestamps, scoring status and the last synchronization time.

These records are used to display your WHOOP values and workout history. The app retrieves them directly from WHOOP's official API to your iPhone. WHOOP values remain identified as such; missing values are not filled in. The connection does not send Apple Health data, Calendar content, check-ins or plans to WHOOP or write health records to your WHOOP account.

Authorization through Supabase: Our authorization service is hosted by Supabase Pte. Ltd. It temporarily processes the one-time authorization code and access and refresh tokens to establish or renew the connection. These tokens are technical access keys to the WHOOP data you authorize. The service's application code writes no token database or token files and contains no application logging of authorization codes, tokens or request and response bodies. Its response contains only the tokens and their validity period and is marked against HTTP caching. The service does not receive the WHOOP health records retrieved by the app.

Operating this service involves Supabase processing technical connection and operational data. These may include IP address, approximate location derived from the IP address, transmitted browser and device details, request time, service requested, response status and execution duration. These logs support service delivery, troubleshooting and security. Section 10 describes their retention.

These application safeguards, including the cache instruction, do not mean that the hosting platform has no logs. We have not established that every platform store excludes authorization request and response content. We therefore do not promise that tokens can never appear in provider records. Credentials and individual log contents should never be sent in support messages.

WHOOP receives your sign-in, authorization and subsequent data requests, including technical connection data. WHOOP, Inc. is responsible for processing within your WHOOP account; we are responsible for Cernidia's processing described here. Further information: WHOOP privacy policy and Supabase privacy notice.

5. Calendar, Apple Watch and notifications

With your Calendar permission, Cernidia reads events from selected calendars, particularly their titles, time periods and identifiers. Information about participants, organizers and the presence of meeting links helps assess whether an event can be moved. Processing takes place locally. The app changes an original event only after your explicit confirmation; any subsequent synchronization by your calendar provider follows that provider's settings.

The iPhone and Apple Watch exchange the day blocks, including their titles, check-ins, health-consent status and Smart Wake settings needed for their features through Apple's device connection. During a workout you start, short-lived derived heart rate and exertion information may be sent to the iPhone. Current derived values may be shared locally between the app and its widgets. If you enable Lock Screen widgets or notifications, their content may be visible there; you control this display in Apple Settings.

Reminders and Smart Wake alarms are scheduled on your devices. Cernidia does not use its own push notification service for them.

6. Storage and retention

Cernidia marks its local app database, WHOOP copy, Watch cache and widget file for exclusion from device backups and uses operating-system file protection. It does not provide app-data cloud synchronization. Apple treats the backup-exclusion flag as guidance, so this is not a guarantee that files can never be included in a backup or restored to a device. The flag and local deletion do not retroactively erase existing backups. WHOOP access and refresh tokens use the iPhone's device-bound Keychain setting. Apple Health's own synchronization, backups and original records are governed separately by your Apple settings. Further information: Apple backup guidance and Apple: Health App and Privacy.

• Daily Health summaries, manual workouts and the WHOOP copy: a rolling window of up to 60 days.
• Derived capacity history: the current day and up to 180 preceding days.
• Stress check-ins and activation notes: a 90-day window, pruned when a new entry of the same kind is saved.
• Energy check-ins and planning history: a window of up to 365 days.
• Tasks, routines, preferences and remaining comparison values: until you delete them through the available app functions or remove the app and its data.
• WHOOP tokens: until renewal, replacement or disconnection. Revoking access in WHOOP ends authorization but does not automatically erase the local copy.
• Health-consent receipt in updated app versions: the statement version, consent time and, if withdrawn, withdrawal time are retained locally until replaced by a new consent or removed with the app's local state. This receipt contains no Health measurements or WHOOP token.

Time-limited records are pruned when next processed, particularly when the app starts, loads or updates data. If you stop opening the app, local files are not deleted solely because time has elapsed. These periods apply to Cernidia's copies, not the original data in Apple Health or WHOOP.

7. Withdrawing access and deleting data

In Cernidia, Settings → Privacy & data → Clear local health summaries, followed by Clear local summaries and confirmation, clears saved health summaries, related health check-ins and notes, the manual workout diary and derived context. This action keeps your health-processing consent and source connections; it does not delete the separate WHOOP copy or revoke Apple Health permission. Connected sources can therefore supply data again. To stop new Apple Health reads, disconnect Apple Health in Cernidia or revoke its read permissions in Apple Health. To withdraw health-processing consent entirely, use the separate withdrawal action described below.

Use Settings → WHOOP → Disconnect WHOOP and confirm Disconnect and delete saved WHOOP data to remove local WHOOP records and tokens. Cernidia also attempts to revoke access at WHOOP. If this fails, for example without an internet connection, the app tells you; remove Cernidia's authorization in WHOOP settings as well. If the connection has expired or access was revoked directly in WHOOP, saved records may still remain. If you have current health-processing consent in Cernidia, the withdrawal described below removes that WHOOP copy as well as the other local health data. If the withdrawal control is missing, contact support as described below. It does not delete the originals in your WHOOP account.

Updated consent controls: the app prepared for public release offers an explicit consent screen before health processing and Settings → Privacy & support → Withdraw consent and delete health data. This stops new health processing in Cernidia, disconnects Apple Health in the app and removes saved health summaries, health-related check-ins and notes, the workout diary and the local WHOOP connection, including its tokens and saved records. Tasks and routines remain. If this control is missing in an older installed beta, disconnect the sources and contact us by email to withdraw consent. A change to this website does not update an installed app.

An offline Apple Watch receives an in-app withdrawal when it reconnects with the iPhone. Stop an active Cernidia workout on that Watch yourself in the meantime. Uninstalling the app is not a reliable way to revoke WHOOP authorization or clear its device Keychain tokens; disconnect before uninstalling and remove the authorization in WHOOP if needed.

You can change Calendar and notification permissions in Apple Settings. You can continue using the app without these permissions; dependent features will be unavailable or limited. Removing Cernidia does not replace revocation in your WHOOP account. Delete original Health, WHOOP and Calendar records at their respective source.

8. Legal bases

• Optional health processing: your explicit consent under GDPR Articles 6(1)(a) and 9(2)(a). This covers Apple Health, the WHOOP connection and health-related check-ins and insights.
• Requested app functions and related support: GDPR Article 6(1)(b), where processing is necessary to provide the service. Optional Calendar access relies on your consent under GDPR Article 6(1)(a).
• Technical operation, security and troubleshooting: GDPR Article 6(1)(f). Our legitimate interests are a reliably available service protected against misuse and the resolution of errors. This also covers the necessary analysis of TestFlight diagnostics and handling of general inquiries.
• Legal obligations: GDPR Article 6(1)(c), where specific retention or documentation duties apply.

Permission in Apple Health or WHOOP authorizes technical access to the data you allow those services to share. It does not automatically replace any required explicit consent to Cernidia's processing of those data. Consent must be freely given and informed. Reading this policy or simply continuing to use the app does not constitute consent.

Providing health data, check-ins and Calendar data is neither a legal requirement nor a condition for using the basic functions. You may withdraw consent at any time for the future using the settings described above or by email. Withdrawal does not affect the lawfulness of processing before it was withdrawn.

9. TestFlight and support

When you use the beta through TestFlight, Apple automatically collects crash logs and usage information and makes them available to us. These may include device model and identifier, operating system details, app version, installations and sessions. Depending on the invitation method, your name and email address may also be visible. You may additionally choose to send feedback and screenshots. We use these details to support the beta and resolve errors. See Apple: TestFlight and Privacy.

If you email us, we process your address, message and any attachments to handle your request. Our email is received through GMX. Please do not send passwords, access tokens, complete Health exports or unnecessary sensitive content.

We delete our own copies of support messages, TestFlight feedback and diagnostics after the inquiry or error is resolved, unless a specific legal retention duty or necessary legal defense requires otherwise. Apple's own retention and deletion options follow its linked TestFlight notice.

9a. No product analytics

Cernidia does not record or send app usage events and does not create an installation or session identifier for that purpose. There is no analytics choice in onboarding or corresponding setting. Local analysis of the health signals you select is separate. Technical connection and operational data for optional WHOOP sign-in and website visits is described in the following sections.

10. Website and technical logs

This website is hosted by Netlify, Inc. Visiting it involves processing technical data such as IP address, time, requested page, response status and transmitted browser details to deliver the pages, identify faults and prevent attacks. We do not add analytics or advertising cookies or scripts to these pages. Further information: Netlify privacy policy.

Retention of technical logs at Netlify and the Supabase authorization service depends on the period needed for operation, troubleshooting and abuse prevention, and on the contractual and technical provisions of the hosting provider. Logs relevant to a specific security incident may be needed until it is resolved and, where applicable, to establish or defend legal claims. The local 60-day periods do not apply to these hosting logs. Disconnecting WHOOP or deleting local app data does not retroactively remove those logs.

At our last verified account check on October 4, 2026, the Supabase organization used the Free plan. Supabase's published pricing currently lists one day of API and database log retention for that plan. This is not a confirmed deletion period for every function, security or backup record. We do not retain a separate copy of individual hosting logs. Further information: Supabase log-retention information, Supabase processing terms and Netlify processing terms.

11. Recipients and processing outside the EEA

Recipients, within the scope described, are WHOOP for the WHOOP feature you connect, Supabase for our authorization service, Apple for its system services and TestFlight, Netlify for the website and our email provider for support. Hosting services process the data needed to provide their services on our behalf; WHOOP and Apple are responsible for their own account and platform services. We do not share local health insights for advertising.

Processing may take place outside the European Economic Area, particularly in the United States; Supabase Pte. Ltd. is based in Singapore. We therefore do not promise exclusively European processing of all connection data. Supabase's Data Processing Addendum provides for EU Standard Contractual Clauses for relevant international transfers. Netlify explains its transfer mechanisms in section 5 of its privacy policy. WHOOP's and Apple's respective linked notices also apply to their processing. You can contact us for further details and information about the applicable safeguards.

12. Your rights

Subject to the legal conditions, you have rights of access, correction, deletion, restriction, data portability and withdrawal of consent. Where we rely on legitimate interests, you may object under GDPR Article 21 on grounds relating to your particular situation.

Contact cernidia@gmx.de to exercise your rights. We cannot remotely access app contents stored only on your devices; we can help you use the available settings to view and delete them. You can still contact us about Cernidia's processing.

You may complain to a data protection authority, particularly in your country of habitual residence, place of work or place of the suspected infringement. The authority responsible for our location is the State Commissioner for Data Protection of Lower Saxony, Germany.

13. Changes to this policy

We update this policy when features or processing change. The current version and its date appear on this page. Changing this text alone does not authorize new processing that requires your consent.