Crime-tracking app Citizen now alerts users to Covid-19 infection risk

At the start of the Covid-19 pandemic, contact tracing was considered the best hope for getting people back to offices and schools safely without a vaccine. The tech industry was optimistic that apps would provide a faster, more effective alternative to the usual painstaking human process of calling and interviewing the networks of infected people to figure out possible sources of exposure.

It hasn’t worked out that way. All efforts in the US are so nascent that Citizen, known for location-based crime alerts, on Thursday launched a feature called SafePass that it’s already calling the largest private contact-tracing network, with only