Privacy policy for Zementio

Overview

This privacy policy applies to the Android app “Zementio – Lighter than Cement”. Zementio works without an account and without a server of its own: everything you enter stays on your device. As the developer, I receive no data from you; the app contains no ads, no analytics or tracking tools and sends no crash reports.

Data leaves your device only when you have the AI estimate calories: either from a photo of your meal or, when entering a meal by hand, from the name and amount you type in. The app then sends these details directly to OpenAI, using your own OpenAI API key (see below).

The website you download the app from is covered by the general privacy policy.

Controller

Kai Röhr, contact details in the legal notice.

Data on your device

Zementio stores in its private storage on your device:

• your meals (name, calories, portion size, time) and favorites,
• your calorie target and, if you fill in the questionnaire, your answers (age, height, weight, sex, activity, goal),
• data from Health Connect, if you allow the connection (see below),
• settings such as language, theme, chosen AI model and the daily cost limit,
• your OpenAI API key, encrypted with a key from the Android Keystore,
• the photos of your meals; they are deleted automatically at the end of the day, the entry stays.

Photos in the gallery: If you switch it on in the settings, the app also saves the photos to your device’s gallery (album “Zementio”). The app does not delete these copies; they are subject to what your gallery does with them, for example a backup by Google Photos.

The app does not take part in Android’s backup, so your data does not end up in a cloud backup automatically. If you uninstall the app or clear its data in Android’s settings, everything is gone.

Your own backup: Under Settings → Backup you can export all data except the API key to a file. The file is saved only where you choose in the file picker, for example a cloud folder of your choice. It contains health data; keep it accordingly safe.

This processing takes place on your device only; I have no access to it.

Camera

Zementio uses the camera only to photograph meals, and only when you open it in the app. Android asks for your permission once.

Calorie estimates by OpenAI

For an estimate, the app sends directly from your device to OpenAI’s programming interface (api.openai.com):

• for an estimate from a photo: the photo of the meal (reduced in size) and, if the AI asks for it, another photo, for example of a nutrition label, your answers to the AI’s questions and the app’s language,
• for “AI estimate” in the dialog for entering a meal by hand: the meal name you type in and, if already entered, the weight or amount.

Your questionnaire answers, your weight and the data from Health Connect are not sent to OpenAI. As with any internet connection, OpenAI also receives your IP address. The app deletes uploaded photos from OpenAI as soon as the estimate is finished or cancelled.

The requests use your own OpenAI API key and are billed to your OpenAI account. That makes you OpenAI’s customer, and processing at OpenAI, including how long OpenAI keeps requests, is governed by the terms and privacy policy of your OpenAI account: https://openai.com/policies/. OpenAI may also process data in the USA. I receive nothing from these requests.

Data is only sent when you yourself send a photo for an estimate or tap “AI estimate”, and only with your own API key to your own OpenAI account. The app explains what is sent when you first set it up. You initiate the transfer yourself; I am not involved in it and receive none of this data. If you do not want to send anything, use neither: meals can also be entered entirely by hand without anything going to OpenAI.

The AI’s answers are marked as AI results in the app. They are estimates, not medical advice.

Health Connect

If you allow it in the app, Zementio reads your burned calories (active and total), your basal metabolic rate, your weight and their history from Health Connect. The app writes nothing to Health Connect. The values it reads are stored on your device only and used to show your calorie target and progress; they are not passed on to anyone, including OpenAI. You can revoke the permission at any time in Health Connect’s settings.

Use of data from Health Connect adheres to Google’s Health Connect policy, including its limited use requirements.

Your rights

As I receive no data from you, I cannot hand over, correct or delete any: only you control your data, in the app and on your device. For data at OpenAI, please contact OpenAI. In general, you have the rights under Art. 15 to 21 GDPR and the right to lodge a complaint with a data protection supervisory authority (Art. 77 GDPR). For questions, you can reach me at the email address given in the legal notice.

Changes

If the app changes in a way that processes different data, I will update this policy.

Last updated: November 2026