Privacy Policy

Effective: 15 August 2026
Last updated: 15 August 2026

This Privacy Policy applies to the mobile application Doomsday (the "App") for iOS devices, developed by Leon Grimmeisen ("we", "us").

1. Controller

The controller within the meaning of the General Data Protection Regulation (GDPR) is:

Leon Grimmeisen
Herderstraße 33b, 22085 Hamburg, Germany
Email: lmgrimmeisen@gmail.com

2. Data minimisation

The App is built around data minimisation. Using it requires no registration, no user account and no personal data. Your lessons, answers, drill results, rating, streak and settings are stored locally on your device and are not transmitted to us.

In addition:

• No location data: the App does not access your location and collects no geolocation data.
• No advertising: the App contains no advertising, uses no advertising identifier (IDFA) and shows no App Tracking Transparency prompt.
• No cross-app tracking: we do not track you across other companies' apps or websites, and we do not sell or share data with data brokers or for advertising purposes.
• No artificial intelligence: the App uses no AI technology to process or analyse your data.

You can erase your locally stored progress at any time in the App under Settings → "Delete all training data". Deleting the App from your device removes all local data as well.

The processing described in the sections below takes place only where you use the relevant feature (in-app purchase, Game Center, reminders) or where you have given your consent (usage analytics).

3. Usage analytics with Mixpanel (only with your consent)

Only with your express, prior consent do we use the analytics service Mixpanel (provider: Mixpanel, Inc.) to understand how the App is used and to improve it. Before you give consent, no analytics data whatsoever is collected, stored or transmitted (opt-in). You are asked once, during onboarding.

• Data processed: a pseudonymous, device-based identifier (the "distinct_id" assigned by Mixpanel) together with pseudonymous usage and interaction events describing how the App is operated – for example which lessons are started and finished, which drills and game modes are played, answers correct and average response time, settings changed, screens viewed, and the purchase and paywall history. Technical information such as app version, build configuration and device type is processed alongside it. This data is pseudonymous, not anonymous: events can be attributed to a device via the identifier, but not to a person known by name. No names, no email addresses, no advertising identifier (IDFA) and no cross-app or cross-provider tracking data are collected.
• Purpose: analysis of product usage in order to improve the App.
• Legal basis: your consent (Art. 6(1)(a) GDPR in conjunction with § 25(1) TDDDG).
• Consent & withdrawal: collection starts only after you have agreed; without consent no analysis takes place. You may withdraw your consent at any time with effect for the future – in the App under Settings → "Share usage data" (turn the switch off). Withdrawal is as easy as giving consent; after withdrawal no further events are transmitted.
• Processor & server location: Mixpanel, Inc. Processing takes place primarily on servers in the European Union (EU endpoint api-eu.mixpanel.com, data centre Amsterdam, Netherlands).
• Transfer to the USA: where the US parent company Mixpanel, Inc. accesses the data in the course of processing, that access is safeguarded by appropriate guarantees: certification under the EU-US Data Privacy Framework and, in addition, the European Commission's Standard Contractual Clauses (SCCs).
• Retention: event data is stored according to the retention settings configured in our Mixpanel project (currently a maximum of 5 years) and deleted automatically thereafter.
• Further information: Mixpanel Privacy Policy.

4. In-app purchase (RevenueCat)

The App offers one optional in-app purchase, Doomsday Pro – a single one-time unlock, not a subscription. We use the service RevenueCat to process and manage that purchase and to restore it on your other devices.

• Data processed: purchase and transaction information, and a randomly generated, pseudonymous app user identifier used to manage your entitlement (Pro unlocked or not). The payment itself is handled exclusively by Apple; we receive no payment data such as card numbers.
• Purpose: providing, unlocking and restoring purchased features.
• Legal basis: performance of the contract of use (Art. 6(1)(b) GDPR).
• Link with analytics: if – and only if – you have consented to usage analytics, the pseudonymous Mixpanel identifier described in section 3 is passed to RevenueCat once, so that purchases and product usage can be evaluated together. Without consent, no such link is created. Neither identifier is connected to a name, an email address or an Apple ID.
• Processor: RevenueCat, Inc. (USA). Further information: RevenueCat Privacy Policy.

5. Game Center leaderboards (optional)

The App offers optional leaderboards through Apple Game Center. These are operated entirely by Apple – we run no server and no account system of our own, and we store no leaderboard data.

• Data processed: if you are signed in to Game Center with your Apple ID, the App submits your Doomsday Rating and your Daily Challenge score to Apple, and displays the rankings Apple returns, including the public Game Center nicknames of other players. Your Apple ID itself is never disclosed to us.
• Purpose: displaying rankings and comparing scores with other players.
• Legal basis: performance of the contract of use (Art. 6(1)(b) GDPR) where you use the feature.
• Optional: the App is fully usable when signed out of Game Center; no score is then submitted. You control Game Center, including your visibility and nickname, in the iOS Settings under "Game Center".
• Further information: Apple Privacy Policy.

6. Daily reminder (local notifications)

You can enable an optional daily reminder. It is scheduled entirely on your device by iOS. There is no push server and no message of any kind is sent to us or to a third party; whether a reminder is due is decided on the device from your locally stored activity. You may revoke the notification permission at any time in the iOS Settings.

7. Apple App Store

The App is distributed through the Apple App Store. In the course of the download and your use of the App Store, Apple may collect data of its own. We have no influence over this. Information on Apple's processing can be found in the Apple Privacy Policy.

8. Contacting us by email

If you contact us by email, the details you provide (email address, name if given, content of the message) are used solely to deal with your enquiry.

Legal basis: Art. 6(1)(b) GDPR (steps prior to a contract) or Art. 6(1)(f) GDPR (legitimate interest in answering enquiries).

Retention: email correspondence is deleted once the enquiry has been dealt with, or after any statutory retention periods have expired.

9. Your rights

Where data of yours is processed, you have the following rights under the GDPR:

• Right of access (Art. 15 GDPR)
• Right to rectification (Art. 16 GDPR)
• Right to erasure (Art. 17 GDPR)
• Right to restriction of processing (Art. 18 GDPR)
• Right to data portability (Art. 20 GDPR)
• Right to object (Art. 21 GDPR)
• Right to withdraw consent with effect for the future (Art. 7(3) GDPR)
• Right to lodge a complaint with a data protection supervisory authority

To exercise your rights, contact us at: lmgrimmeisen@gmail.com

Please note that the identifiers described above are pseudonymous and are not linked to your name. To act on a request concerning analytics data we may therefore need the identifier from your device in order to find the relevant records.

10. Children

The App is not directed at children under 13, and we do not knowingly collect data from them. Usage analytics is off by default and requires an explicit opt-in. If you believe a child has provided us with data, please contact us and we will delete it.

11. Changes to this Privacy Policy

We may update this Privacy Policy as required. The current version is always available on this page. In the event of material changes, the "Last updated" date above will be adjusted accordingly.

12. Contact

For any questions about data protection, reach us at:
lmgrimmeisen@gmail.com