On a personal level, whether you are contagious will affect your behavior—for example, whether you decide to visit relatives in a nursing home or maternity ward.
The app currently being developed by Inria and several European partners aims to help identify people who may be infected without knowing they are infected. How does it work? Your mobile phone is assigned a set of cryptographic identifiers, which change every 15 minutes. Whenever it comes sufficiently close to another phone, that phone, if the app is enabled, retrieves your current cryptographic identifier and sends you its own. These pairs of identifiers, which record a contact, are sent to a server each day. If someone tests positive and reports it through the app, the server retrieves all the identifiers belonging to that person's contacts. All the associated phones then receive an alert indicating the likelihood of infection. Yet no one learns the identity of the virus carrier or the place or date of the encounter. In fact, this information is not even known, since the protocol relies solely on Bluetooth communications between devices. More details at www.inria.fr
