Around the world, a diverse and growing chorus is calling for the use of smartphone proximity technology to fight COVID-19. In particular, public health experts and others argue that smartphones could provide a solution to an urgent need for rapid, widespread contact tracing—that is, tracking who infected people come in contact with as they move through the world. Proponents of this approach point out that many people already own smartphones, which are frequently used to track users’ movements and interactions in the physical world.

Tracking and tracing patients with mobile phone apps and other electronic devices already has been used in China, South Korea and several other countries