Jon Masters reports the Commonwealth has enabled a system that is supposed to alert people with Android or Apple phones if they come within infecting distance of people who have reported being infected with Covid-19.
The system works by using Bluetooth to collect and share IDs with other phones that have the system turned on - and alert you if any of them belong to people who've tested positive (and then reported it via the system).
On Android phones, go into Settings, and then Google. Click on Exposure Notifications, then select United States under Active Region. Select Massachusetts, then follow the remaining prompts to enable the system on your phone. On an iOS phone, go into Settings, then Exposure Notification.
More on MassNotify.