On April 1, 2020, Apple released its free COVID-19 Screening Tool, a simple app with resources to help you figure out what to do next if you think that you might have COVID-19. Less than two months later, Apple released iOS 13.5, an update to the iPhone operating system that added support for exposure notification apps, a simple form of contact tracing. That iOS update was only half of what was required for this system to work; additionally, each country or — in the U.S. — each state had to have its own exposure notification app that worked with the notification system first released in iOS 13.5.
I live in New Orleans, and Louisiana has just released its exposure notification app, which Louisiana calls COVID Defense. Zac Hall of 9to5Mac has been tracking these apps, and based on his count, similar apps are now available in Alabama, Arizona, California, Colorado, Connecticut, Delaware, Hawaii, Maryland, Michigan, Minnesota, Nevada, New Jersey, New York, North Carolina, North Dakota, Pennsylvania, Virginia, Washington, Wisconsin, Wyoming, and the District of Columbia. That makes Louisiana the 21st state (plus D.C.) to have one of these apps. Additional states, such as Oregon, should be up-and-running soon.
I'm going to describe Louisiana's app in this post, but all of the similar apps from other states and countries work the same way because they are all based on the same technology jointly developed by Apple and Google. Note that some states, such as California, take advantage of a system called Exposure Notification Express that works the same way but you don't have to download a special app; you just receive a notification asking if you want to opt-in.
The way that the app works is that it generates a unique, anonymous token associated with your iPhone but not associated with your name, location, or any other personal information. The token changes every 10-20 minutes. Whenever your iPhone senses (using Bluetooth) that it is somewhat close to another iPhone or Android phone running the same app, your iPhone saves the token from that other device. And it keeps a list of all of those tokens for 14 days.
If a person tests positive for COVID-19, they will receive (or can obtain from the Louisiana Department of Health) a verification code. That person should enter that code in the COVID Defense app on their device. Every day, the app downloads a list of all of the tokens associated with positive COVID-19 cases and checks them against the list of tokens it has encountered in the last 14 days. If there is a match, then your iPhone will give you a push notification alerting you of a potential exposure. Note that, to ensure your privacy, all of the matching takes place on your individual iPhone. The government is not notified of your possible exposure; only you are notified.
The notification will not tell you the name of the infected person or the location where you were possibly exposed because — to protect privacy — Apple and Google built the app not to store any of that information. Thus, nobody has to worry about the app tracking their location or anything like that. The tradeoff is that it makes the alert less useful because you don't know much about the potential exposure, but the point is simply that it gives you a warning of a potential exposure so that, hopefully, you will get tested. Even if you are not (yet) experiencing any symptoms, you may be an asymptomatic carrier of the virus as a result of your recent exposure.
Obviously, this app will not alert you to all exposures. For the app to work well, you need for the people around you to be using the app. According to an AP report from a month ago, in 16 jurisdictions in which the app was available in 2020, about one in 14 people in those jurisdictions used the app. That same article reports that 45% of people in Finland used a similar app. A report from Jennifer Valentino-DeVries in the New York Times last month said that 60% of the population in the District of Columbia is participating. It would be better to see larger use everywhere, but at least there are still many millions of people taking advantage of this technology.
Additionally, for the app to be helpful, you need for anyone who tests positive to be thoughtful enough to log their positive status into their own app. According to that same New York Times article, a recent study in Switzerland concluded that for every 100 people who tested positive, the app correctly notified 24 contacts who had caught the virus.
I wish that Louisiana had released their app long ago so that, by now, there might be a larger user base in my state. Nevertheless, I guess better late than never, and by releasing an app at the end of January 2021, Louisiana is still ahead of over half of the other states in the United States. If an app like this (or the built-in service) is available wherever you live, I encourage you to use it. The more people who do so, the better we are all protected.
Click here to get COVID Defense (free): 
