The pitch from technology companies goes something like this: We can tap phone data to track Covid-19 infections in U.S. communities and swiftly warn people about potential exposure, all without ever compromising anyone’s privacy. Casey Ross writes in STAT that Apple and Google turned heads a few days ago when they announced a joint effort to bolster this public health service — a task known as contact tracing — by building software into smartphones that relies on Bluetooth technology to track users’ proximity to one another. Facebook is participating in a similar effort led by the Massachusetts Institute of Technology. While their brands give them instant credibility in the business world, infectious disease experts aren’t convinced the technology offers a tidy solution to such a complicated public health problem.