Google and Apple phones would quietly in the background create a database of other phones that have been in Bluetooth range—about 100 to 200 feet—over a rolling two-week time period. When users find out that they are infected, they can send an alert to all the phones that were recently in their proximity. The broadcast would not identify the infected person, it would just alert the recipient that someone in his or her recent orbit had been infected. And, importantly, the companies say they are not collecting data on people’s identities and infection status. Nearly all of the data and communication would be stored on users’ phones.

... But building a data set of people who have been in the same room together... is not without risk of exploitation... [T[he companies have only submitted framework proposals for a service they say will roll out in May... Advantages [are]... it's opt in... it's anonymous...it's mostly decentralized... no personal information is required for use... Disadvantages [are]... it's vulnerable to trolls...[and] spoofing... false alerts could weaken trust in the system... other apps may try to grab the data... some location information may be exposed to the central server...anonymous data is always vulnerable to being re-identified...it relies on testing which is currently inadequate.