Opendoor only collects data that is used for functionality. It uses Google Firebase Cloud Messaging SDK to get notified about state changes.
By using the Firebase SDK the Firebase Installation ID (FID) is generated and collected. It can't be used to uniquely identify a user or physical device. The ip address is collecte as well, apparently for debugging purposes.
It collects and transmits the Application Version for topic subscription and unsubscription and the Firebase user agent.
It collects device metadata, like the OS version, name, model, brand and form factor. Furthermore it knows the app the app was installed with, like the Google Play Store. Also the used Firebase SDKs with versions are known.
For more information have a look at Firebase Privacy
Privacy: We only save log files of the web server (ip addresses of the visiting devices) for seven days.