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What are COVID-19 exposure notifications and how do they work?

Your smartphone may have the ability to notify you if you've been exposed to COVID-19 by a total stranger. All you have to do is turn this technology on.
Twenty states, Guam and Washington, D.C., have exposure notifications in some capacity enabled for their residents.
Twenty states, Guam and Washington, D.C., have exposure notifications in some capacity enabled for their residents.TODAY Illustration / Getty Images
/ Source: TODAY

Contact tracing is a crucial part of preventing the spread of the coronavirus, but this process of finding and notifying people who've been exposed to someone with COVID-19 requires time and government resources — not to mention it's even more challenging when there is community spread.

The Centers for Disease Control and Prevention currently defines a close contact with an infected person as someone who's been within 6 feet of a COVID-19-positive person for more than 15 minutes in a day. That means an extended trip to the grocery store or workout at a public gym could fit the bill, if you're near the same people for more than just a few minutes total.

To help identify these at-risk individuals and ease the contact-tracing burden on local public health authorities, Google and Apple worked together to create the Exposure Notification System, which relies on smartphones and Bluetooth to assess when an infected person has exposed someone else.

The two tech giants announced they'd be working on such a system in April, and in August, the first state, Virginia, launched an app deploying it. Here's a guide to exposure notifications, including how they work, turning them on, and what to know about your privacy.

What is an exposure notification?

Simply put, exposure notifications alert individuals (who have exposure notifications activated) on their phone if they've been a close contact of a COVID-19-positive person who also has exposure notifications activated.

The exposure notification pops up like a regular notification on your phone's screen. It will also include instructions from your local health authority about what to do next and how to keep yourself and the people around you safe.

Depending on where you live and what kind of smartphone you have, you can activate your exposure notifications by downloading an app or through your phone's settings.

How do exposure notifications work?

The Exposure Notification System uses Bluetooth Low Energy (BLE), which requires less power than traditional Bluetooth, so your smartphone can exchange signals with other smartphones near you. The strength of the signal determines a rough estimate of the distance between the two phones and, presumably, the people carrying them, explained Nader Moayeri, research scientist at the National Institute of Standards and Technology (NIST).

With the system that Apple and Google created, no personal data from your phone is tracked or shared, not even your location, Google told TODAY in a statement. The technology is able to do that by having the nearby phones exchange keys of random numbers with each other. Your own phone's key changes every 10 to 20 minutes, according to Google, so you can't be identified by your phone's key.

Dudley Carr, the creator of Nevada's exposure app, COVID Trace, explained how this process works by comparing the keys being exchanged to raffle tickets because both have no personally identifying information. Imagine that you have a string of raffle tickets, as does another person in the same room as you. You hand each other your raffle tickets, as a way to know you were near that other person. Then, if you test positive, the exposure notification system can alert anyone who has your raffle ticket numbers stored on their phone. Phones store each string of numbers for 14 days, according to Google.

Local public health authorities determine what signal strength (and therefore proximity) and duration constitutes a close contact, Google told TODAY. If you test positive, you can choose whether to notify your close contacts, defined by your state's notification system's algorithm, from the 14 days before you were tested. Simply turning on exposure notifications doesn't mean your phone will automatically do this, Emma Sudduth, consultant at the Association of Public Health Laboratories (APHL), told TODAY.

In order to report yourself through your phone, you need a verification code from your local health authority, Google said, usually provided via phone call or text. If a close contact of yours tests positive, you'll be notified anywhere from 15 minutes to 24 hours after that person chooses to report him or herself, Sudduth said.

How accurate are exposure notifications?

Moayeri and Google both stressed that that BLE is not a perfect technology because signal strength doesn't exactly correlate to distance. For example, you may be 30 feet away from someone, but your phone could pick up a strong signal from theirs because there's nothing obstructing the path between you two. On the other hand, you could be a few feet away from someone, but a third person could walk between you two, weakening the signal.

These two scenarios could result in you being notified when you weren't actually within 6 feet of someone or not being notified when you were, Moayeri said. "We are trying to quantify that, how frequently these two types of errors happen," he added.

Which states have them?

At this stage, there are 17 states and territories that have exposure notifications, according to Google. These are:

  • Alabama
  • Colorado
  • Connecticut
  • Delaware
  • Guam
  • Maryland
  • Michigan
  • Minnesota
  • Nevada
  • New Jersey
  • New York
  • North Carolina
  • North Dakota
  • Pennsylvania
  • Virginia
  • Washington, D.C.
  • Wyoming

In addition, five states are currently piloting exposure notification systems with limited populations. If you are part of one the limited populations within the state, you can activate them. These states are:

  • Arizona
  • California
  • Hawaii
  • Oregon
  • Washington

Most of these 22 states and territories, but not all, rely on a server hosted by the APHL for their exposure notification systems. These states are "interoperable," Sudduth said, meaning that if you travel from one state to another and are exposed on your trip, you can still receive a notification, even though it didn't happen in the state with which your notification system is associated. In order for this to work, though, both states must use the server hosted by APHL.

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The APHL has a list of these states and territories on its website. In addition to these, APHL is working with Virginia and Arizona to transition them to the server hosted by APHL, Sudduth said.

How to turn on exposure notifications

The path to turning on your exposure notifications depends on where you live and what kind of smartphone you have. To start, you need to live in one of the above states or territories for your exposure notifications to work to their fullest capacity. That is to say, it's possible to download an app for a state you don't live in, but you won't be able to report if you test positive because your own public health authority won't be able to provide you with an applicable verification code.

Turning on exposure notifications for iPhone

If you have an iPhone, you can activate your exposure notifications by tapping on your settings icon and scrolling down. When you see the line that reads "Exposure Notifications," tap on it, and it will ask you to select your country and state or region. If your region has a separate app, it will direct you to the app store to download it. Within the app, you can then agree to enable the technology that allows your keys to be shared with other phones and stores other phones' keys.

How to turn on exposure notifications on an iPhone.Courtesy of Google

If your region doesn't have its own app but is still on the above list, your phone will give you the option to "continue" and then agree to the terms and enable the technology without downloading an app.

If your state is not on the above list, your phone can alert you if exposure notifications do become available. Tap settings, then "Exposure Notifications," and then turn on "Availability Alerts."

Turning on exposure notifications for Android

If you have an Android, you need to download your state or region's official app to activate exposure notifications, according to Google. Your phone will ask you to agree to turn them on, and then you'll be able to open the app.

How to turn on exposure notifications for Android.Courtesy of Google

To activate the notifications, you need to turn on your Bluetooth, unlike with iPhones. For Android 10 and earlier, your location setting must also be on in order for your phone to scan for Bluetooth signals. Your exposure notification app will not collect or track your location, according to Google.

Should I be concerned about my security?

Google stressed in its statement to TODAY that "Google and Apple put user privacy at the forefront of this exposure notification technology’s design and have established strict guidelines to ensure that privacy is safeguarded. The choice to use this technology rests with the user, and they can turn it off at any time in Settings."

It added that "Apple and Google will not receive identifying information about the user, device location data, or information about any other devices the user has been in proximity of."

Maoyeri cautioned that there's no such thing as "perfect privacy," but he feels the system Apple and Google have created provides an adequate degree of protection.

How can exposure notifications prevent the spread?

Contact tracing, to the degree necessary for the COVID-19 epidemic, creates a tremendous burden on state and local health authorities, Jeff Stover, executive advisor to the Virginia health commissioner, told TODAY.

"This is not easy work," he explained. "How often do you answer your phone if a number just calls and you don't recognize that number? How often do you answer your door when someone knocks and you see it's someone you don't know? These are things that we, just by default, ignore. From a contact-tracing standpoint, it can be very difficult to get your job done in today's world."

As a result, exposure notifications can help "get the word out to people" that they should consider getting tested or changing their behavior while assessing their symptoms, Stover said. For people who live or work with high-risk individuals, this is "incredibly powerful," he added.

That exposure notifications may alert an exposed individual faster than a human contact tracer is another major advantage, according to Becker.

"Early detection saves lives. The sooner you learn you may've been exposed, the quicker it is that you can take actions to protect yourself, get a test and then protect others," he said. "Just like getting a test or washing your hands, every little thing that we do together makes a big thing."