As coronavirus cases surged worldwide in March, Fitbit observed a global decline in physical activity among its 30 million activity tracker and smartwatch users. As governments implemented shelter-in-place orders, the company recorded a nearly 20 percent decline in weekly step counts in New York and San Francisco. The pandemic may be hampering regular fitness routines, but now Fitbit is exploring whether its wearable devices could help researchers predict if users have a coronavirus infection before they even notice any symptoms.