Warn-App-Companion is a free Android app designed to help users better understand COVID-19 risk exposure. Developed by Michael Huebler, this lifestyle app falls under the Health & Fitness subcategory and is compatible with Android 9.0. The app is programmed to read the Rolling Proximity IDs of the user's device, which can be exported from the RaMBLE app or microG, without root access. If the app has root access, it reads the IDs from the device's database. The app then downloads the positive keys from the selected countries' Warn-Servers, including Germany, Denmark, Ireland, Italy, Croatia, Latvia, the Netherlands, Poland, Spain, and Cyprus, among others. The app compares the two and displays the risk encounters, including the time, signal strength, and risk level.

The app does not process any personal data and only accesses the internet to download data from the Warn-Servers. It does not send any data to other servers and does not display any ads. In RaMBLE mode, the app can display the location of the risk encounter. The app is open-source, and the source code is available on GitHub. The app is purely for personal use and does not serve any commercial purposes.