Fig. 2: Contact tracing for COVID-19 with Bluetooth-enabled smartphone apps.
From: Digital technologies in the public-health response to COVID-19
Proximity-detecting contact-tracing apps use Bluetooth signals emitting from nearby devices to record contact events. Centralized apps share information about contacts and contact events with a central server. The centralized TraceTogether app72 uploads information when a user reports testing positive for COVID-19. Some centralized Bluetooth-enabled contact-tracing apps upload the contact graph for all users148. Decentralized apps, such as SwissCovid149, upload only an anonymous identifier of the user who reports testing positive for COVID-19. This identifier is then broadcast to all users of the app, which compares the identifier with on-phone contact-event records.
