COVID-19 News

Lincoln Lab team designing system for COVID-19 contact tracing

A team led by researchers from MIT and Lincoln Laboratory, as well as partners from many institutions, is developing a digital "contact tracing" system that uses smartphone signals to determine an individual's movement patterns leading up to a positive COVID-19 diagnosis, allowing other users of the system to determine whether they might have crossed paths with the infected person.

The system is designed to augment "manual" contact tracing by public health officials, while preserving the privacy of all individuals. It relies on short-range Bluetooth signals that represent random strings of numbers, likened to “chirps” that other nearby smartphones can remember detecting.

If a person tests positive for COVID-19, they can upload the list of chirps their phone has put out in the past 14 days to a database. Other people can then scan the database to see if any of those chirps match the ones picked up by their phones. If there’s a match, a notification will inform that person that they may have been exposed to the virus, and will include information from public health authorities on next steps to take. Vitally, this entire process is done using cryptographic techniques to maintain the privacy of those who are Covid-19 positive and those wishing to check if they have been in contact with an infected person.

This approach to private, automated contact tracing will be available in a number of ways, including through the privacy-first effort launched at MIT in response to Covid-19 called SafePaths. This broad set of mobile apps is under development by a team led by Ramesh Raskar of the MIT Media Lab. The design of the new Bluetooth-based system has benefited from SafePaths’ early work in this area.

Smartphones already have the ability to advertise their presence to other devices via Bluetooth. Apple’s “Find My” feature, for example, uses chirps from a lost iPhone or MacBook to catch the attention of other Apple devices, helping the owner of the lost device to eventually find it.

“Find My inspired this system. If my phone is lost, it can start broadcasting a Bluetooth signal that’s just a random number; it’s like being in the middle of the ocean and waving a light. If someone walks by with Bluetooth enabled, their phone doesn’t know anything about me; it will just tell Apple, ‘Hey, I saw this light,’” says Marc Zissman, the associate head of MIT Lincoln Laboratory’s Cyber Security and Information Science Division and co-principal investigator of the project.

With their system, the team is essentially asking a phone to send out this kind of random signal all the time and to keep a log of these signals. At the same time, the phone detects chirps it has picked up from other phones, and only logs chirps that would be medically significant for contact tracing — those emitted from within an approximate 6-foot radius and picked up for a certain duration of time, say 10 minutes.

Phone owners would get involved by downloading an app that enables this system. After a positive diagnosis, a person would receive a QR code from a health official. By scanning the code through that app, that person can upload their log to the cloud. Anyone with the app could then initiate their phones to scan these logs. A notification, if there’s a match, could tell a user how long they were near an infected person and the approximate distance.

The ability to conduct contact tracing quickly and at a large scale can be effective not only in flattening the curve of the outbreak, but also for enabling people to safely enter public life once a community is on the downward side of the curve. Francis Collins, director of the National Institutes of Health, discussed the benefits and challenges of digital contact tracing in his April 9 Director's Blog (

Collins mentioned that NIH grantee Trevor Bedford, of the Fred Hutchinson Cancer Research Center in Seattle, and colleagues just launched NextTrace, a project that aims to build an opt-in app community for “digital participatory contact tracing” of COVID-19. NIH also has a team that is actively exploring the kind of technology that could achieve the benefits without unduly compromising personal privacy, Collins wrote.

Read more about the MIT-Lincoln Lab project here: