This policy explains what information the duoBooks app (for iPhone, iPad and Android) and the duo-books.com website collect, why we collect it, who we share it with, and what choices you have. Please also read our Terms of Use.
The short version
We collect what duoBooks needs to work: your sign-in details, the words you save, the books you import, and how you use the app.
We don't sell your data, and there are no ads in duoBooks.
When you tap a word or sentence, that text is sent to AI and translation services to create the translation.
You can delete your account from inside the app at any time.
1. Who we are
duoBooks is published under the name PlainProg on the App Store and under the name Petro Darchyn on Google Play. In this policy, "we", "us" and "our" mean Petro Darchyn (PlainProg). We are responsible for your personal data in duoBooks (we are the "controller").
If you have any question about privacy, email us at [email protected].
2. What we collect
You can use much of duoBooks without an account: you can read books and translate within the free limits. Some features need you to sign in. Here is what we collect, and when.
Account information
When you sign in, we create a duoBooks account with a user ID.
Sign in with Apple (iPhone and iPad): we receive your Apple user ID and, the first time you sign in, your name. We don't ask Apple for your email address.
Sign in with Google (iPhone, iPad and Android): we receive your email address and your name.
duoBooks doesn't use passwords, so we never see or store one.
What you save and your learning activity
When you are signed in, we store:
the words and quotes you save, with the sentence they came from and the title and author of the book;
the translations, notes, tags and sections in your dictionary;
your flashcard history: which words you know, learn or review, and when;
the books you like and the collections you create;
your native language and the language you are learning;
your reading activity for Insights: which book you read, for how long, and how many words and sentences you translated;
whether you want review reminders.
Your reading position in a book stays on your device. We don't collect it.
Books you import
If you import your own EPUB or FB2 book while you are signed in, the app uploads the file to our cloud storage, together with its title, author, cover and file name, so that it appears in your library. We don't show your books to other users. If you import a book while you are signed out, it stays on your device.
Text you translate or listen to
To translate and read aloud, the app sends these to our servers:
the word or sentence you tap, with the sentences around it (up to about 60 words before and after it), so that the translation fits the context;
the sentences you open in Deconstruct;
the text you play aloud;
the word you type in "All forms" search inside a book;
short samples of a book's text, to detect its language.
We send the languages involved together with this text. Section 5 explains what happens next.
Purchases
If you buy Full Access, Apple or Google handles the payment. We never see your card or bank details. Apple or Google sends us details of the purchase: the plan, the transaction or purchase ID, the dates, whether it renews, and the country and price. We link the purchase to your duoBooks account, so that your subscription works on all your devices. To do this, Apple or Google receives a code that contains your duoBooks user ID.
Device and technical information
A device identifier. The app creates it from your device's own identifier (on iPhone and iPad, the ID that Apple gives our apps; on Android, the Android ID) and scrambles it before sending it. We use it for the device limit of subscriptions and, on Android, for the free translation limits.
A push-notification token and your time zone, when you are signed in, so that we can send review reminders at a sensible time if you allow notifications.
Technical details sent with requests: on iPhone and iPad, the app version, the iOS version and your preferred languages; on both platforms, the app's interface language and your translation language.
Your IP address, which every internet service receives. We use it to deliver the service and keep it secure. We don't store it in our database.
Your App Store or Google Play country, to adapt the book catalog to your region and to suggest your languages.
Error reports and feedback
If a book fails to open on iPhone or iPad, the app may send us the book file and its location on your device, even if you are not signed in, so that we can fix the problem.
If Google sign-in fails on Android, the app sends us technical details: the app version, the device maker and model, the Android version, the error, and your user ID if you have one.
If you tell us what we can improve in the app's rating screen, we receive your message and your user ID.
Usage analytics
We use Google Analytics for Firebase to understand which features people use, so that we can improve duoBooks. It records events such as opening a book, translating a sentence or opening the subscription screen. With these events, it collects an app-instance ID, your device model, operating system, app version, language and approximate location (country or city, estimated from your IP address). We never send it your name, email address, user ID, book titles or the text you read.
On Android, Google Analytics also collects your device's advertising ID. We don't use it for advertising. You can reset or delete it in your phone's settings (usually Settings → Privacy → Ads, or Settings → Google → Ads). On iPhone and iPad, Google Analytics doesn't collect the advertising ID.
When you contact us
If you email us, we receive your email address and whatever you write.
What we don't collect
duoBooks doesn't access your contacts, photos, camera, microphone or precise location, and it never reads your clipboard.
3. How we use your information
To run duoBooks: sign you in, sync your dictionary, collections and imported books, and show your Insights.
To translate, explain and read aloud the text you choose.
To run your flashcards and send the review reminders you asked for.
To process subscriptions, make them work on your devices, and apply the device limit and the free limits.
To adapt the catalog to your languages and region.
To find and fix bugs and to improve duoBooks.
To prevent abuse and keep duoBooks secure.
To see, in total numbers, how well our ads for duoBooks work (see section 7).
To answer your messages.
We don't sell your personal data, and we don't use it to show you ads. We don't make decisions about you that have legal or similarly significant effects based only on automated processing.
4. Legal bases (EEA and UK)
If you live in the European Economic Area or the United Kingdom, we rely on these legal bases:
Contract: to provide the features you use, including your account, translations, your dictionary and subscriptions.
Legitimate interests: to analyse how duoBooks is used, fix errors, keep the service secure and prevent abuse. You can object at any time (see section 10).
Consent: for push notifications, which you allow or refuse in your device settings. You can withdraw your consent at any time.
Legal obligation: when the law requires us to keep or share information.
5. Translation and AI
duoBooks uses AI to translate. Our servers send text to AI, machine-translation and text-to-speech providers when you translate something (a word, a sentence or a book description), open Deconstruct, play text aloud, save a word or quote, or search for all forms of a word, and when the app needs to detect the language of a book. The providers send back the translation, explanations, examples, audio or the detected language.
We send only the text, the languages and settings such as the voice, never your name, email address or user ID.
The providers process this text under their own terms and policies.
We don't use your text to train AI models.
We may keep sentence translations in a cache that is not linked to you, so that the same sentence is translated faster next time.
Don't import documents that contain confidential or sensitive personal information, because their text is sent for translation when you tap it.
AI can make mistakes. Translations and explanations may be wrong.
6. Who we share information with
We share personal information only with service providers that help us run duoBooks, and only what they need:
Google: cloud file storage (Google Cloud Storage), Google Analytics for Firebase, Firebase Cloud Messaging (notifications), Google Sign-In and Google Play (payments).
Apple: Sign in with Apple and App Store payments.
AI, machine-translation and text-to-speech providers: to translate text and read it aloud (see section 5).
Hosting providers: our servers and databases run on rented servers.
We may also share information:
when the law requires it, or to protect the rights, safety and security of our users, the public or us;
if duoBooks is sold or transferred to a new owner, who would then have to protect your data as this policy describes.
We don't sell your personal data.
7. Advertising our app
There are no ads inside duoBooks. We do advertise duoBooks itself on Google and in the App Store (Apple Search Ads). Google and Apple give us only total numbers, such as how many people installed duoBooks after seeing an ad. We don't link your duoBooks account or what you do in the app to these ads.
8. International transfers
Our servers and our service providers store and process data in several countries, including countries of the European Union and the United States. These countries may have different data-protection laws from the country where you live. When we transfer your data, we send each provider only what it needs, and we choose providers that publish data-protection commitments.
9. How long we keep your data
Your account data (your profile, dictionary, flashcard history, collections, Insights and imported books): as long as your account exists. When you delete your account, we delete it within 30 days (see section 11).
Purchase records: after you delete your account, we keep them without your name or email address for as long as we need them to handle refunds, disputes and fraud, and to meet legal obligations.
Error reports and feedback: only as long as we need them to fix problems and improve duoBooks.
Device counters for the free limits: as long as we need them to apply the limits. They are not linked to your account.
Analytics data: Google keeps it for at most 14 months.
The translation cache: it is not linked to you, and we may keep it to make translations faster.
Emails: as long as we need them to answer you and keep a record of our conversation.
10. Your rights and choices
Depending on where you live, you may have the right to:
see the personal data we hold about you and get a copy of it;
correct it;
delete it;
receive it in a format you can move to another service;
object to or restrict how we use it, including for analytics;
withdraw your consent at any time.
To use these rights, email [email protected]. We may ask you to confirm that the account is yours. We answer within one month.
If you think we have not handled your data correctly, you can complain to the data-protection authority in the country where you live or work.
Your choices in the app and on your device:
Use duoBooks without an account: reading, translating within the free limits and importing books to your device don't need one.
Notifications: turn review reminders off in the Learn Words settings or in your phone's settings.
Advertising ID (Android): reset or delete it in your phone's settings.
Your account: delete it at any time (see section 11).
11. Deleting your account
In the app (iPhone, iPad and Android)
Open the Account tab.
Tap Log Out.
Tap Delete My Account.
Confirm with Delete.
Without the app
Email [email protected] with the subject "Delete my account". Send it from the Google address you use in duoBooks. If you use Sign in with Apple, tell us your user ID (the app shows it on the Log Out screen) or the name on your account. We may ask for details to confirm that the account is yours.
What we delete, and what we keep
Within 30 days, we delete your profile and sign-in details, your dictionary (words, quotes, notes and tags), your flashcard history, likes and collections, your imported books, your Insights, your settings and notification tokens, and the error reports and feedback linked to your account.
We keep:
records of your purchases, without your name or email address (see section 9);
device counters for the free limits, which are not linked to your account;
the translation cache, which is not linked to you;
analytics data at Google, which is not linked to your name or email address and is deleted after at most 14 months.
Good to know
Deleting the app doesn't delete your account.
Deleting your account doesn't cancel your subscription. Cancel it in your App Store or Google Play settings.
Books and data saved on your device stay there until you delete the app.
12. Children
duoBooks is not directed at children under 13, and you must be at least 13 to use it. In the EU and the UK, if you are under 16, use duoBooks only with a parent's or guardian's permission. If you think that a child under 13 has given us personal data, email us and we will delete it.
13. Security
The app talks to our servers over encrypted connections (HTTPS), and we limit access to personal data to what is needed to run duoBooks. No system is completely secure, so we can't guarantee absolute security. If we learn of a data breach that affects you, we will tell you and the authorities when the law requires it.
14. Our website
The duo-books.com website doesn't use analytics or advertising cookies, and it doesn't ask for personal information. Its pages load fonts from Google Fonts, and some pages show videos from YouTube (in privacy-enhanced mode) and Vimeo. When a page loads, these providers receive your IP address and browser details under their own privacy policies. Our servers also receive your IP address when you visit.
15. Changes to this policy
We may update this policy when duoBooks changes. We will change the date at the top. If a change is significant, we will give notice on this page, and in the app where possible, before the change takes effect.