I spent the last month becoming a connoisseur of digital contact tracing approaches since this seems like something where I might be able to help. Many other people have been thinking along similar lines (great), but I also see several misconceptions that even smart and deeply involved people are making. For the following a key distinction to understand is between proximity and location approaches. In proximity approaches (such as DP3T , TCN , MIT PACT(*) , Apple or one of the UW PACT(*) protocols which I am involved in) smartphones use Bluetooth low energy and possibly ultrasonics to discover other smartphones nearby. Location approaches (such as MIT Safe Paths or Israel ) instead record the absolute location of the device based on gps, cell tower triangulation, or wifi signals. Location traces are both poor quality and intrinsically identifying Many people associate the ability of a phone to determine where it is with the ability to discover where it is with high precision. Th...