Skeptics worry the apps will amount to a high-tech distraction. But so far, we only have epidemiological models to suggest such apps can help control an epidemic. The idea is that such digital contact tracing will identify people potentially exposed to the coronavirus who should self-isolate-and that they'll voluntarily do so.

Two million people downloaded it in the first 24 hours it was available. 'The more people who download this important public health app … the sooner we can safely lift restrictions and get back to business and do the things we love,' he said in a 26 April press release. Last month, when the Australian government launched a smartphone app called COVIDSafe to find and alert the contacts of people infected with the coronavirus, Prime Minister Scott Morrison made a hard sell to the public. Science's COVID-19 reporting is supported by the Pulitzer Center.