Privacy Policy

Last updated: April 15, 2026

The short version: Tandem helps you switch between an ebook and audiobook without losing your place. Your books stay on your device. The only network service Tandem uses is a short audio transcription request to line up reading and listening when needed. We don't have accounts, don't track you, and don't store your books on any server.

Data We Collect

Tandem collects no personal information. Specifically:

No account or login required. No name, email, or identifying information is ever requested.
No analytics or tracking. Tandem contains no analytics SDKs, crash reporters, or advertising frameworks.
No cloud storage of your books. Your EPUB and audiobook files are stored locally on your device only.

Data Stored Locally on Your Device

Data	Where stored	Why
Imported EPUB files	App Documents container	Library persists across launches
Imported audio files	App Documents container	Paired audiobooks persist
Reading progress	App Documents container	Resume where you left off
Sync anchors (paragraph → audio time)	App Documents container	Makes switching between reading and listening accurate
Reader settings	UserDefaults / iCloud preferences	Preferences persist and sync across your Apple devices

This data never leaves your device unless you explicitly export or share a file yourself using the iOS/macOS share sheet.

Network Services

Audio transcription for reading-listening sync

To line up your ebook and audiobook when you switch modes, Tandem sends short audio clips (typically 10–30 seconds) from your audiobook to OpenAI's Whisper transcription service. The service returns a text transcript which Tandem uses to locate the matching part of your ebook.

Only audio from files you have imported is ever sent.
Only short clips are sent, not entire audiobooks.
Transcription results are cached on your device so repeated syncs of the same passage do not require new network calls.
OpenAI's processing of this data is governed by their privacy policy. Per their API data usage policy, audio submitted through the API is not used to train their models.

No other network activity

Tandem makes no other network requests. There is no telemetry, no analytics, no remote configuration, no content sync, and no advertising.

Permissions

Speech Recognition (on-device, iOS only)

When available, Tandem can use Apple's on-device SFSpeechRecognizer as an alternative to the OpenAI service. This runs entirely on your device. No audio or transcription data is sent to Apple or any other service when on-device recognition is used.

Microphone

Tandem never records from your microphone. The microphone usage description in Info.plist is required by iOS/macOS for apps that link SFSpeechRecognizer, but no live microphone audio is ever captured.

Third-Party Open Source Packages

Package	Purpose	Privacy impact
ZIPFoundation	Parsing EPUB files (ZIP archives)	None — runs on-device
swift-kindle	Kindle format support	None — runs on-device

Children's Privacy

Tandem collects no personal information from any user, including children under 13. The app is appropriate for all ages.

Changes to This Policy

If this privacy policy changes, the "Last updated" date above will reflect the change. Significant changes will also be noted in the app's release notes.

Contact

Questions about this privacy policy: privacy@tandembooks.co