This post is part of a series on contact tracing apps. You can read our introduction to the series and get links to the other entries here.

Over the last several weeks, governments, private enterprises, and academics across the US have announced plans to develop contact tracing mechanisms to help combat the spread of COVID-19. 

We've previously discussed how these work, but we'll repeat here for convenience. Imagine you’re in the midst of an earlier pandemic: the 1918 flu. As you go through your day, you ask for and write down the names of everyone you encounter in a notepad. At first, you don’t give the list to anyone, and in fact, your notepad never leaves your jacket pocket. 

Meanwhile, if anyone comes down with COVID-19, that person can voluntarily notify the local newspapers, who then publish a daily list of everyone who’s self-reported. Each morning you sit down with the newspaper in one hand and your list in the other, and cross-check to see if you’ve come into contact with anyone who’s tested positive. If you find a match, then you can take steps to self-quarantine or otherwise manage your exposure. 

At its core, the tracing mechanisms works exactly the same way. Except that, instead of asking for and writing down names, people’s phones are constantly looking for other phones in proximity (sometimes by broadcasting Bluetooth signals to everyone around them, sometimes by GPS). And instead of exchanging names, everyone exchanges anonymous identifiers that can’t easily be traced back to anyone. The result is a respectably privacy-minded system to help people figure out whether they’ve been exposed.

For the most part, government in the US has left leadership for this initiative in the hands of private enterprise and academia. MIT was an early leader in promoting ideas about how privacy-friendly contact tracing would work. It has since produced the Safe Paths app in collaboration with Harvard and others. To determine proximity, that app relies primarily on GPS signals. 

Meanwhile, a team working across Stanford University (the finest university in the universe, according to one of this post's authors) and the University of Waterloo is producing Covid Watch. In contrast to Safe Paths, Covid Watch determines proximity using Bluetooth signals. 

Major US tech companies are also racing to develop and deploy their own contact tracing apps. It's worth noting that these various initiatives are not necessarily competing with one another: the Safe Paths and Covid Watch teams are collaborating on parts of their respective technologies, and major tech players are often developing their apps in co-ordination with academic institutions. 

On the other hand, governments have largely stayed out of the picture. One exception that proves the rule is Utah, which plans to launch an app called Healthy Together. Unlike other apps, this would provide more information back to state government on the spread of the virus. And Healthy Together is not strictly a Utah-government app. It will be available to other state governments as well.

Other posts in this series: