[rct42]

They've released their open-source version of the app, OpenTrace

https://github.com/opentrace-community/

Interesting in the Android version they request ACCESS_FINE_LOCATION (i.e., access to GPS) instead of ACCESS_COURSE_LOCATION (i.e., access to BLE). They have also include Firebase analytics (which captures city-level location data) into the app as well.

[bogomipz]

Wouldn't bluetooth be preferable to GPS since GPS requires a direct line of sight? And Singapore being an urban area with underground mass transit and lots of shopping malls I would have though that bluetooth would provide better accuracy of contact/proximity.