Technologies to rapidly alert people when they have been in contact with someone carrying the coronavirus SARS-CoV-2 are part of a strategy to bring the pandemic under control. Currently, at least 47 contact-tracing apps are available globally (see go.nature.com/2zc1qhk). They are already in use in Australia, South Korea and Singapore, for instance. And many other governments are testing or considering them.
Here we set out 16 questions to assess whether — and to what extent — a contact-tracing app is ethically justifiable. These questions could assist governments, public-health agencies and providers to develop ethical apps — they have already informed developments in France, Italy and the United Kingdom. They will also help watchdogs and others to scrutinize such technologies.