TechCrunch:

Apple and Google’s engineering teams have banded together to create a decentralized contact tracing tool that will help individuals determine whether they have been exposed to someone with COVID-19.

Contact tracing is a useful tool that helps public health authorities track the spread of the disease and inform the potentially exposed so that they can get tested. It does this by identifying and “following up with” people who have come into contact with a COVID-19-affected person.

The system uses on-board radios on your device to transmit an anonymous ID over short ranges — using Bluetooth beaconing. Servers relay your last 14 days of rotating IDs to other devices, which search for a match. A match is determined based on a threshold of time spent and distance maintained between two devices.

If a match is found with another user that has told the system that they have tested positive, you are notified and can take steps to be tested and to self-quarantine.

Even though it’s opt-in, I predict that when this comes online in May, it will be a controversial move.