Many countries and researchers are promoting the use of contact tracing apps to help limit the spread of COVID-19 and aid in the eventual recovery, but they may require slow manual tracing or a sacrifice in privacy (say, warning when a patient leaves home). MIT researchers think they have a solution with few compromises. They’re developing a system, PACT (Private Automatic Contact Tracing), that promises to automatically trace contacts while keeping identities secret.

The system would send Bluetooth “chirps” of random numbers to nearby phones. If a person tests positive for COVID-19, they can upload all their received chirps from the past 14 days (about the maximum incubation time) to help others find out if they were close by. If there’s a match between numbers, the passers-by get notifications telling them of possible contact and what to do next. The very nature of the process continuously changes IDs, making it difficult or impossible to link data to a given individual. There’s no GPS, phone numbers or other information people could use to guess who you are.