Privacy Policy
Effective Date: April 26, 2026
String Tension AI ("we," "our," or "us") provides an iOS application that measures tennis string tension using acoustic analysis via your iPhone's microphone. We are committed to protecting your privacy and being transparent about how your data is handled. This Privacy Policy explains what information we collect, how we use it, and your choices regarding your data.
1. Information We Collect
Microphone Audio
Our app requests access to your iPhone's microphone to capture the sound produced when you tap or pluck a tennis string. Audio captured by the microphone is processed entirely on your device and is never transmitted to our servers or any third party. Audio data is analyzed in real time to determine string tension and is immediately discarded after processing — no raw audio recordings are stored.
Measurement Data
When you perform a tension measurement, the app creates a record that may include:
- Calculated tension value (in lbs)
- Frequency analysis results and confidence score
- Timestamp of the measurement
- Associated racquet and string setup profiles you have created
Racquet and String Profiles
You may choose to create profiles for your racquets and string setups. This includes information you voluntarily provide, such as racquet model, string type, gauge, and reference tension.
Playing Sessions
You may choose to log playing sessions to track how your string tension changes over time. These records may include session dates, associated racquets, string setups, measurements, and notes you enter in the app.
iCloud Sync Data
App data such as racquets, string setups, measurements, notes, preferences, and related records may sync through Apple iCloud/CloudKit if iCloud is enabled for your Apple ID. This data is stored in your private iCloud database and is governed by Apple's Privacy Policy.
Purchase Information
If you purchase a Pro upgrade or other in-app purchases, all payment processing is handled entirely by Apple through the App Store. We do not receive, process, or store any payment card details or billing information.
Optional Analytics, Crash Reporting, and Remote Configuration
String Tension AI includes Firebase services for optional analytics, crash reporting, and remote configuration. Analytics and crash reporting are disabled by default and are enabled only if you choose to allow them in the app's privacy settings. Firebase Remote Config may fetch configuration values used to adjust app behavior.
Information We Do Not Collect
We do not collect your name, email address, phone number, location data, contacts, photos, browsing history, or any other personal information beyond what is described above. We do not use advertising SDKs or social media tracking tools.
2. Data Types We May Collect
Depending on your settings and app usage, we may collect:
- Diagnostics, such as crash data and performance data, for app stability and troubleshooting.
- Product interaction data, such as feature usage and app events, for analytics if you opt in.
- App configuration and rollout metadata used to deliver or evaluate feature configuration.
3. How We Use Your Information
The data described above is used exclusively to:
- Perform real-time acoustic analysis and calculate string tension
- Store and display your measurement history and trends
- Generate AI-powered restring recommendations based on your data
- Sync your data across your Apple devices via iCloud
- Enable data export in CSV and PDF formats
- Improve app stability and troubleshoot crashes if you opt in to crash reporting
- Understand app feature usage and events if you opt in to analytics
- Deliver local defaults or remote configuration values used to adjust app behavior
We do not sell your personal data. We do not use your data for third-party advertising. We do not use Firebase data to track you across apps or websites owned by other companies.
4. Data Storage and Security
On-Device Storage
All measurement data, racquet profiles, string setups, playing sessions, and other user-created records are stored locally on your device. The app uses standard iOS data storage mechanisms that benefit from the device-level encryption provided by your iPhone.
iCloud Storage
When iCloud sync is enabled, app data such as racquets, string setups, measurements, notes, preferences, and related records is stored in your private CloudKit database within Apple's CloudKit infrastructure, which encrypts data both in transit and at rest. iCloud/CloudKit storage is separate from Firebase analytics, crash reporting, and remote configuration.
Audio Data
Microphone audio is processed in real time within the app's memory and is never written to disk, transmitted over the network, or stored in any persistent form. Once a tension reading is calculated, the underlying audio data is immediately released from memory.
5. Data Sharing and Third Parties
We do not sell your personal data.
The third-party services that may interact with your data are:
- Apple iCloud (CloudKit) — for syncing your data across your devices, governed by Apple's privacy policy
- Apple App Store — for processing in-app purchases, governed by Apple's privacy policy
- Apple Crash Reporting — if you have opted into sharing diagnostics with app developers in your iOS settings, we may receive anonymized crash reports to improve app stability
- Firebase / Google — we use Firebase Analytics, Firebase Crashlytics, and Firebase Remote Config
Firebase / Google
Firebase Analytics may collect de-identified app interaction and usage events when analytics consent is enabled. Exact measurement values are rounded into broad ranges before collection — no precise tension readings or personal performance data leave your device.
Firebase Crashlytics may collect crash reports, non-fatal error reports, stack traces, device information, operating system information, app version, and related diagnostic context when crash reporting consent is enabled.
Firebase Remote Config may fetch configuration values used to adjust app behavior. When used with analytics-enabled features, Firebase may use app instance or analytics data to support configuration targeting and rollout measurement.
Google Privacy Policy: https://policies.google.com/privacy
Firebase privacy and data disclosure information: Firebase Privacy and Security and Firebase Apple privacy details.
We do not integrate advertising networks or social media tracking tools.
6. Your Rights and Choices
Microphone Access
You can revoke microphone permission at any time through your iPhone's Settings app (Settings > Privacy & Security > Microphone). Without microphone access, the app cannot perform new tension measurements but will continue to display your existing data.
Analytics and Crash Reporting Consent
Analytics and crash reporting are opt-in. You can change your choices at any time in the app's Settings. If you do not opt in, String Tension AI uses local defaults and does not intentionally send analytics or crash reports through Firebase.
Data Export
The app allows you to export your measurement data in CSV and PDF formats, giving you full portability of your information.
Data Deletion
You can delete individual measurements, racquet profiles, string setups, or playing sessions within the app. To delete all data, you may uninstall the app, which removes all locally stored data. To remove iCloud-synced data, you can manage your iCloud storage through iOS Settings.
For Users in the European Economic Area (GDPR)
If you are located in the EEA, you have the right to access, rectify, erase, restrict processing of, and port your personal data. Since all data is stored on your device or in your personal iCloud account, you have direct control over your data at all times. For any GDPR-related requests, contact us at the email below.
For Users in California (CCPA)
California residents have the right to know what personal information is collected, request deletion, and opt out of the sale of personal information. We do not sell personal information. For any CCPA-related requests, contact us at the email below.
7. Children's Privacy
String Tension AI is not directed at children under the age of 13. We do not knowingly collect personal information from children under 13. If you believe a child under 13 has provided us with personal information, please contact us and we will take steps to remove such information.
8. Changes to This Policy
We may update this Privacy Policy from time to time. When we make changes, we will update the "Effective Date" at the top of this page. For significant changes, we may also provide notice within the app. We encourage you to review this policy periodically.
9. Contact Us
If you have any questions or concerns about this Privacy Policy or our data practices, please contact us at: