CORONAVIRUS CASES are surging, temperatures are dropping, and Thanksgiving is approaching. This is a recipe for mass infection. Many Americans are taking pains to weather the winter season as responsibly as possible, but there is something more we can do to help ourselves and each other — and it only takes a few taps on a smartphone screen.

Hopes for digital contact tracing soared in the spring, but attention sputtered as time ticked on. Rather than a national rollout early on as in other countries, citizens here were treated to a state-by-state approach. Initially the hang-up was privacy: How could you build a system that tracked encounters among civilians without tracking those civilians, too? Apple and Google eventually developed a strategy for devices to exchange “handshakes” via Bluetooth, relying only on proximity and not location, and storing everything on individuals’ phones instead of in a centralized government database. A Marylander who enrolls, in other words, isn’t handing his sensitive data over to Gov. Larry Hogan (R) — or to Silicon Valley.

This privacy protection initially introduced new wrinkles. The two tech companies had started calling their tool “exposure notifications” for a reason; take the ability of the government to harness the system for identifying at-risk individuals out of the equation, and it isn’t really contact tracing anymore. All the tool does is tell people when they’ve been close to someone who has chosen to report a positive diagnosis. But right now, that may be exactly what people need. Evaluating our own “bubbles” of close contacts amid this crisis is easy enough, but figuring out who our close contacts’ close contacts are, and so on, is tougher. Especially as indoor interaction increases and as traveling ticks up despite Centers for Disease Control and Prevention guidance, our bubbles could turn more porous than we know.

Thankfully, Apple and Google made their software easier for states to use this fall by allowing health agencies to harness it without building customized apps. Now, at least 18 states and territories, including D.C., Maryland and Virginia, have some version of the service in place. When Virginia Gov. Ralph Northam (D) tested positive for the coronavirus in September, the members of his staff exposed to him received pings on their devices. Some states send push alerts automatically to iPhones; in others, users must go into their settings and toggle on exposure notifications; in others, they must download a stand-alone app. The information on how to enroll is generally available on state websites. And soon, the tools should start working across state lines.

These apps won’t fix everything, but that doesn’t mean they can’t help with anything. Powerless as we may often feel in this pandemic, those of us with smartphones do have power over this much: a tool to stem the spread of the coronavirus that sits in our pockets, waiting to be tapped.

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