A phone app that will tell you if you’ve been exposed to coronavirus is about to launch in Colorado. Here’s how to use it.

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Colorado is hoping to dramatically expand its coronavirus contact-tracing and notification capacity starting this weekend, with the launch of a new phone application that can alert someone if they’ve been exposed to the virus — but only if people opt into it.

“This is a game-changer for us in Colorado,” said Sarah Tuneberg, the leader of Colorado’s Containment and Testing Team, which worked with tech companies Apple and Google to make the service available.

People in Colorado will begin receiving push notifications on their phones on Sunday telling them that the long-promised, long-delayed app, called Exposure Notification, is available. The app will be automatically installed on Apple phones, and people will be given the option of turning it on through their phone’s settings menu. The app will need to be downloaded to phones that use Google’s Android operating system, with a link to do so provided in the push notification.

The app uses Bluetooth technology to exchange anonymous “tokens” with nearby phones that have also enabled the app. When someone who uses the app tests positive for coronavirus, they can send a notice to everyone whose phone their phone recently exchanged tokens with. That notice will tell the contact the date of their possible exposure and instruct them to begin quarantining immediately, while also providing a link to information about where to get tested for the virus.

Tuneberg said the app doesn’t track people’s locations and the tokens don’t record any other personal information. People can enable or disable it at any time.

“We want to ensure that everybody maintains control of all of their experience here,” she said.

Here’s a few more questions and answers on the app.

How exactly do I turn on the app?

The push notification will give you the instructions you need to activate the app. The Colorado Department of Public Health and Environment produced some short videos showing how this will work.

For Apple phones:

And for Android phones:

How much does it cost?

The app is free to users. Since it runs off of Bluetooth, it also doesn’t use a lot of mobile data, said Jenny Wanger, a founding member of the Linux Foundation for Public Health, which helped develop the app. An internet connection is only needed for a user to receive the notification that they may have been exposed or to notify others following a positive test result. The exchanging of tokens does not use mobile data, she said. 

Apple and Google are providing the service to the state at no cost.

What does it track?

Wanger said the app doesn’t track personally identifying information. It won’t tell you, for instance, where you might have been exposed or whom you came into contact with. It will simply tell you if your phone has been in close proximity to the phone of someone who later tested positive for coronavirus and it will tell you on what day that happened.

What happens if I test positive?

After your positive test is reported to public health authorities, a contact-tracer will reach out to you and ask if you have the Exposure Notification app activated. If you do, they will send you a link that gives you the option of sending out a notification to people who have been near your phone. Again, the app will not tell people your name or any other identifying information, Tuneberg said.

It should look like this:

Tuneberg said, though it’s voluntary, the state is hopeful people will choose to step up to be part of this system in an effort to slow the spread of COVID-19.

“We ask you to add your phones to the fight against COVID,” she said.

What happens if I was exposed?

You will get a notification, which will tell you the day of your possible exposure and will provide quarantine instructions and a link to information about where to get tested.

It should look like this:

Why does this matter?

Along with mask-wearing and testing, contact-tracing is one of the pillars of the state’s response to coronavirus.

A report last month from the Colorado School of Public Health’s COVID-19 modeling team concluded that contact-tracing has at various points boosted transmission reduction in the state by around 5%.

“Contact tracing likely played a vital role in suppressing transmission and maintaining low levels of hospitalizations over the months of July and August,” the researchers wrote.

But traditional contact-tracing, where a public health worker interviews a person who just tested positive and asks them where they’ve been and with whom they’ve been in contact, has some significant limitations.

For one, it’s time-consuming, meaning that by the time the contact-tracer catches up with someone who may have been exposed, it’s possible the contact has already spread the virus to someone else. People may also refuse to provide information in an interview or not answer their phone when called. And people who are infected may not know the names of everyone they came into contact with — for example, if they were sitting next to a stranger on the bus.

Tuneberg said the hope is that the app covers some of those gaps by working quickly and being able to notify people even if the infected person doesn’t know their names. She said it’s also possible some people might be more comfortable using technology to notify others rather than talking to a person.

A small study has found that this kind of electronic contact tracing, even if it’s adopted by only a small percentage of the population, can still have a measurable impact in slowing coronavirus transmission.

“As we’re seeing cases, hospitalizations and positive test results surge across Colorado, we are so excited to have this new technology in the toolbox to help us fight COVID,” Tuneberg said. “And it can have a marked effect.”