Digital Contact Tracing.

Have now heard several analyses that have doubted that Tracking can work.

How Digital Contact Tracing Could Work in the US, and Why It May Never Happen
By David Cardinal
                                                                                         
It’s widely agreed that re-opening major portions of our economy relatively safely will require an extensive testing and contact-tracing system. Manual contact tracing — where those who test positive are interviewed about recent travel and person-to-person contacts — is expensive, hard to scale, and error-prone. So it is natural to see if digital technologies can help.

There are almost as many different approaches to how that might work as there are countries. But they fall into a few broad categories in terms of which technologies they use, how much data they store, and how they protect privacy. Here’s a look at some of the current and planned efforts, with a focus on those being piloted for deployment in the US.

All Roads Lead to the Smartphone
While there are some limited efforts using dedicated devices that have proven effective in controlled situations such as nursing homes, for broad deployment among the general public the obvious device of choice is the smartphone. Most people have one, they have a broad array of sensors, and they can be programmed to run custom apps. But “most people” isn’t “all people,” and many older phones don’t have the needed capability to run some of the proposed apps. So even phone-based solutions will need to deal with making their platform ubiquitous.

Stanford, Google, Apple: Protecting Privacy Via BLE
 ... Perhaps the most “private” solution being proposed is one that was first publicized as Covid Watch, led by Stanford researcher Christina White and now embraced by the unlikely alliance of Apple and Google. This solution relies entirely on logging anonymized Bluetooth Low Energy (BLE) contacts between two users. Each phone broadcasts a random ID that changes every 10-20 minutes — meaning it should be impossible to use the IDs to track a specific user or find out more about them. At the same time, nearby phones log all the IDs they receive. So far, no data has left anyone’s phone.

When a user tests positive for infection, they can get a code from a medical professional that allows the app to upload the recent (probably last 14 days worth of) random IDs that their phone has broadcast. At least once a day, phones running the app download a full set of “infected” IDs, and compare them with the list they have logged. If there is a match, then the user gets the day, duration, and signal strength of the contact, so they know that they may have come in contact with someone who was infected.  ... "