How phones can alert you to COVID-19 exposure

More than 8.1 million people in the U.S. have turned their iPhones and Android devices into pandemic contact-tracing tools, but it hasn’t been of much use when their neighbors, classmates and coworkers aren’t on the same system. Apple and Google co-created “exposure notification” technology to alert phone users if they spent time near someone who tests positive for the coronavirus, so they know to get tested, too. It’s built with tight privacy restrictions to maintain users’ anonymity, but the tech companies have left it to each state’s public health authority to decide whether to use it. Here’s how it works and where to find it.