It is also a world in which the return to normal is predicated on the introduction of a novel technology. Millions of Americans—many of whom might be deeply skeptical of government surveillance, or Big Tech—may become participants in a national project to track their own movements and interactions, to help public-health experts map out the spread of an invisible enemy.

This is the world of “test and trace.”

In the past month, the coronavirus pandemic has necessitated a deep freeze of U.S. activity. Storefronts are closed, millions of Americans have lost their jobs, and millions more are putting their health at risk in hospitals and grocery stores. This modern nightmare may not truly end until a reliable antiviral treatment or COVID-19 vaccine is widely available.

Until that day, which may be a year or two away, our best hope in the fight against the coronavirus is to play a game of sophisticated Whack-a-Mole that often goes by the name of “test and trace.”

Most readers might have an image of what the testing half entails, with those long nasal swabs that practically scrape the edge of our frontal lobe. The tracing half of the equation is less understood. But it is more likely to leave its mark on American politics and society.

In its most basic form, tracing—otherwise known as tracking, or contact tracing—means identifying all the recent interactions of sick individuals to determine whom they might have infected. Testing plus tracing can besiege the virus, starve it of new bodies, and return the world to its previral routine, or something like it.

Read: You’re likely to get the coronavirus

Until recently, tracing relied on an old-fashioned technology: interviews. To stop the spread of Ebola, authorities from the Centers for Disease Control and Prevention asked sick people to list recent interactions with family, friends, and businesses. That interview would produce a list of contacts, who would be monitored for illness for several weeks. The state of Massachusetts recently announced plans to hire 1,000 people to do these sorts of contract-tracing interviews.

But that old-school approach might not be enough. People have faulty memories about who or what they’ve touched, or where they’ve been. More important, person-to-person interviews might be too slow to arrest a national pandemic accelerating through a population.

The solution? Your phone.

Our cellphones and smartphones have several means of logging our activity. GPS tracks our location, and Bluetooth exchanges signals with nearby devices. In its most basic form, cellphone tracing might go like this: If someone tests positive for COVID-19, health officials could obtain a record of that person’s cellphone activity and compare it with the data emitted by other phone owners. If officials saw any GPS overlaps (e.g., data showing that I went to a McDonald’s hot spot) or Bluetooth hits (e.g., data showing that I came within several feet of a new patient), they could contact me and urge me to self-isolate, or seek a test.