Privacy Policy — Dualex

Last updated: July 16, 2026

1. Introduction

Dualex ("we", "our", "us") is committed to protecting your privacy. This Privacy Policy explains how we collect, use, and safeguard your personal data when you use the Dualex application ("the App").

2. Data We Collect

Account Data: When you create an account, we collect your email address and store it securely using Firebase Authentication.

Learning Data: We store your learning progress, review queue (SM-2 spaced repetition data), placement test results, homework errors, and exam results. All data is isolated per user (scoped by Firebase Auth UID).

Technical Data: We use Firebase Crashlytics and Firebase Performance Monitoring to collect crash reports and app performance metrics. This data is anonymized and used solely to improve app stability.

Voice Data: When you use Text-to-Speech (TTS), audio is streamed from Google Cloud Wavenet. We do not store or record your voice.

3. How We Use Your Data

• To provide and personalize your learning experience (CEFR-aligned lessons, SRS review, exams).
• To track your progress and adapt difficulty using the SM-2 algorithm.
• To send daily review reminders (optional — you may opt out in Profile settings).
• To diagnose and fix app crashes via Firebase Crashlytics.
• To improve app performance via Firebase Performance Monitoring.

4. Data Storage & Security

• All user data is stored in Firebase Firestore in the europe-west3 (Frankfurt) region, compliant with GDPR data residency requirements.
• User data is isolated per unique Firebase Auth UID — no user can access another user's data.
• API keys are stored server-side via Firebase Cloud Functions — never on the client.
• All network traffic is encrypted via HTTPS/TLS.

5. Third-Party Services

We do NOT sell, trade, or share your personal data with any third party for marketing or advertising purposes.

6. Your Rights (GDPR)

If you are in the European Economic Area (EEA), you have the right to:

• Access: Request a copy of your personal data.
• Rectification: Correct inaccurate data.
• Erasure: Delete your account and all associated data.
• Portability: Export your data in a machine-readable format.
• Objection: Opt out of data processing for specific purposes.

To exercise any of these rights, contact us at privacy@dualex.app.

7. Data Retention

We retain your data as long as your account is active. If you delete your account, all your personal data is permanently deleted from Firestore within 30 days.

8. Children's Privacy

Dualex is not intended for children under 13. We do not knowingly collect data from children under 13.

9. Changes to This Policy

We may update this Privacy Policy from time to time. We will notify you of any changes by posting the new policy in the App and updating the "Last updated" date.

10. Contact

For privacy-related inquiries, contact: privacy@dualex.app

11. Account Deletion & Data Removal

You have the right to request the deletion of your Dualex account and all associated personal data at any time.

Option 1: In-App Account Deletion (Immediate)

• Open the Dualex app or visit Dualex Account Deletion.
• Log into your account.
• Navigate to Profile → Delete Account.
• Type DELETE in the confirmation input and click Delete Account.
• Your account, progress, review queue, test results, and Firestore data will be permanently purged immediately.

Option 2: Email Request

If you cannot access the app, email us at privacy@dualex.app or support@dualex.app from your registered email address with the subject "Account Deletion Request". We will erase all account data within 30 days.