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Lara Antal / Verywell

Key Takeaways

  • Exposure Notification is a smartphone-powered tool used to augment traditional contact tracing
  • Users’ phones send and receive non-identifiable Bluetooth keys when people they have come into proximity with for more than 15 minutes test positive for COVID-19
  • Nineteen states have approved the use of this technology, with more likely to come in the future.

Exposure Notification (EN) technology is a rapidly-progressing public health tool developed by Apple and Google to slow the spread of COVID-19. This technology leverages the ubiquity of smartphones to notify users when they have come into contact with someone who has tested positive for the coronavirus. And experts say it the best way to help traditional contact tracing keep up with the pace of modern life in a global pandemic.

Julie Samuels, the Executive Director of Tech:NYC, a non-profit organization that developed COVID Alert NY, tells Verywell that this technology is meant to complement traditional contact tracing, which relies on officials to track and trace people who have had exposure to someone with COVID-19.

“This app is a tool that will help contact tracers increase the availability of contact tracing in the population; it will not replace traditional contact tracing," she says.

Kameka Dempsey, a member of the COVID-19 Technology Task Force, tells Verywell that exposure notifications fill the gaps where conventional methods fall short.

“People don’t remember where they were the day before, let alone for two whole weeks,” she says. “What manual contact tracing doesn’t offer either is the connection with strangers or people we don’t know.”

Who Developed This Technology?

The technology powering these apps was developed by Apple and Google and operates in conjunction with state public health authorities. The two companies developed the technology to be compatible with their mobile operating systems, iOS, and Android, respectively.

As Dempsey notes, state public health authorities then have options on how to deploy this framework.

“There are two paths that you could choose—you can decide to do a custom-built app, or you can use the express version,” she says. “The custom app version is when you get a third-party developer to build an app over the Google and Apple built API.”

The second path, known as EN express, doesn’t require public health departments to develop their own applications.

“On iOS, that’s app-less because it is just turning on a setting inside the operating system on iPhone," she says. "On Android, it’s app-light because it is a Google minted app—the public health authority would give Google the parameters, and then Google does the build for that app using the given settings.”

How to Activate Exposure Notifications

On iOS 13.5 or later:

Go to Settings --> Exposure Notifications --> Turn on Exposure Notifications --> Choose your country and state --> Download the application


On Android 6.0 or later:

Check if an app is available in your region --> Download it from the Play Store --> Follow the in-app instructions

How Does It Work?

The technology is powered by Bluetooth Low Energy, which allows devices to communicate without the use of cellular data or an internet connection. Notably, GPS information is not used, preventing the apps from collecting location data.

Dempsey explains that the critical components of the technology are unique, continuously updated keys produced by each phone, and stored on a centralized key server.

When two individuals remain within a certain distance from each other for an extended period of time, they would be notified if one of them later receives a positive test result. The exact parameters for the distance and duration of contact are set by the individual public health authority. In New York, for example, Samuels tells Verywell that they are set at 6 feet and 10 minutes.

“Let’s say Alice and Bob are sitting on a bench, they don’t know each other, and they have a lengthy conversation sitting just a few feet apart," Dempsey says. "Their phones are exchanging non-identifiable Bluetooth tokens which change frequently while they’re having this conversation. Each phone keeps a local record of the last 14 days of keys received, essentially as a virtual log of all the possible exposures a person has had."

If a few days later Bob receives a positive diagnosis for COVID-19, he would receive a code from his public health authorities which he could input into the app.

Exposure Notification technology relies on people proactively and willingly updating their COVID-19 status in an app.

“Then what happens is, with Bob’s consent, he uploads the last 14 days of his Bluetooth keys to the national key server,” she continues.

During this time, Alice’s phone will be periodically downloading all the encrypted keys from people who tested positive in her region and chose to share their results.

“So then when the match is made between Bob and Alice's key, that’s when she gets an alert, but it doesn’t tell her that it was from Bob; she has no idea who it was,” Dempsey explains.

Mitigating Privacy Concerns

The use of Bluetooth, combined with the constantly changing keys, ensures that no identifiable information is ever transmitted between users.

Furthermore, the key server is a national key server operated independently from Google and Apple. The server is operated by the Association of Public Health Laboratories (APHL) and is kept separate from the developers.

Another key emphasis on privacy is that all decisions require the consent of the user.

“I think it’s important to note about privacy that the user has choice along the way,” Dempsey says. “There are three different points along the way that I like to highlight where an individual has to make the decision to participate in this public health tool.”

  1. First decision point: The decision whether to actually download the app or turn on the settings to activate exposure notifications
  2. Second decision point: Whether or not you do something with the code from public health authorities after testing positive.
  3. Third decision point: Whether or not you agree and consent that you are okay with your code being sent to the key server to perform matching to see if the people that you have been proximate to receive a notification

Why Hasn't This Been Implemented Nationwide?

Currently, only 18 U.S states and the District of Columbia have approved the use of either EN express or their own application utilizing the framework developed by Apple and Google. Globally, over 40 countries have implemented this technology, with more expecting to do so in the coming months.

As Dempsey explains, the structure of public health in the United States has forced a state-by-state implementation of the technology.

“In countries outside the US, it’s one country, one app," she says. "In the U.S., because we don’t have a national public health authority, it has to be federated to the states.”

Despite the states setting their own parameters and, in some cases, making their own standalone apps, all keys are still uploaded to the same national key server, allowing for compatibility across state lines.

Samuels says that despite this decentralized structure, there is still a path for a federal implementation of this technology.

What This Means For You

Exposure Notification cannot collect or share any information about your location or identity outside of your department of health. Check your state’s public health authority to see if they are participating in this technology. Exposure Notification can be an effective tool to increase awareness of potential COVID-19 exposure.

“I am optimistic that the Biden administration will nationalize this, and we will see a national contact tracing app from the CDC,” she says.

There is reason to believe that exposure notification can be an effective tool for combating the spread of COVID-19. A collaborative study between Google, Stanford University, and Oxford University modeled the effect of implementing exposure notification at different adoption levels in three Washington counties. The researchers found that, even at only 15% adoption, total deaths were reduced by up to 6.6%, 11.3%, and 15.0%, in each of the three respective counties.

Samuels tells Verywell that the lack of awareness about exposure notification is a major reason for its slow implementation in the U.S.

“I think the best option would be to call your governor’s office, write letters to the editor of your local newspapers and make some noise that you want this," she says. "The state is going to need some resources to build this, so it is important to put pressure on your state government."

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Article Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Google COVID-19 information & resources. Exposure notifications: using technology to help public health authorities fight COVID‑19.

  2. Association of Public Health Laboratories. Exposure notifications.

  3. Abueg M, Hinch R, Wu N, et al. Modeling the combined effect of digital exposure notification and non-pharmaceutical interventions on the COVID-19 epidemic in Washington state. Epidemiology. 2020. doi:10.1101/2020.08.29.20184135