Here you can find a sample application written in QT as a demonstration of how to use QR codes as indoor beacons. The app reads QR codes and tries to find them in OSM. If it finds a result, the map shows you the coordinate where the QR is located. You can use this to locate a user inside a building.
See the readme for further information.
You can download an build the code or install the arm apk available at Github (https://github.com/GlassOceanos/osm-indoormark-demo-app/releases)
Note that the provided map plugin used in QT only reaches a 18 level zoom and that does not seem enough for an indoor scenario.