How Bluetooth could unleash the world’s largest experiment in digital contact tracing

Your smartphone’s Bluetooth feature could be key in combatting the Covid-19 pandemic.
Your smartphone’s Bluetooth feature could be key in combatting the Covid-19 pandemic.
Image: Willy Kurniawan/Reuters
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Sometime in May, you could receive a smartphone alert from your local health agency saying you may have come into contact with someone who tested positive for Covid-19. Such a warning will be made possible by a feature that is nearly 30 years old: Bluetooth. The same wireless standard that lets you play Spotify playlists in your car or link your smartphone to your wireless earbuds is paving the way for the world’s largest experiment in digital contact tracing.

Contact tracing, or the act of tracking all those who have come into contact with an infected person, is normally a laborious process performed by health officials. It’s been key in slowing down the spread of some of the worst infectious diseases to hit humans, including polio, HIV/AIDs, polio, and Ebola. Now, it’s made easier by the fact that a huge fraction of the world’s population have devices that can track their location.

Since coronavirus hit China, more than a billion people have downloaded Health Code, a smartphone app to track the virus, which runs on several popular platforms, including Alipay and TenCent’s WeChat. The apps generate color codes based on a person’s risk level of contracting the virus, and freely share GPS location and personal data with the police. A similar strategy is being used by Israeli telcos working with their national security agency.

But in the West, privacy concerns and fears of governmental abuse have turned technologists toward Bluetooth instead. Unlike the more invasive data collection efforts led by governments like China and South Korea, Bluetooth is anonymized and decentralized. Smartphones generate short-range Bluetooth signals, which translate to random strings of numbers. These numbers, and not a person’s name or address or location, can be used to identify them.

Singapore became the first nation to use Bluetooth for Covid-19 contact tracing, with an app called Trace Together. There are now dozens of efforts led by global academic institutions and health authorities to create Bluetooth-based digital contact tracing apps.

A team of researchers at Stanford University and the University of Waterloo are working on an app called Covid Watch. At MIT, researchers have created the Safe Paths platform, which uses a hybrid of GPS and Bluetooth.In the EU, a German-led effort known as the Pan-European Privacy Preserving Proximity Tracing technology platform, or PEPP-PT, aims to create an application programming interface (API) for all 27 European member nations. In the UK, NHSX, the national health agency’s digital unit, is testing its own contact tracing app.

Most digital tracing apps will work like this: Your phone will generate a temporary contact number, known as a TCN. If two users with a contact tracing number downloaded come into close proximity (roughly six feet) for a sustained period of time, the two phones will share each other’s TCNs. If one of the users tests positive, they’ll input a special code given by health officials into the app. The app will then alert each person whose phone logged the infected user’s TCN during a specified period of time, likely 14 days.

Proponents of Bluetooth-based digital contact tracing argue that it’s both more private and accurate than using your GPS or cell tower coordinates. Bluetooth, in theory, can identify the person you sat next to on the train for an hour last Monday who later tested positive, while GPS and cell signals may wrongly associate everyone in the car itself as a contact.

It also may be more effective in close quarters. “With Bluetooth, proximity can be approximated by signal strength that is reduced by obstructions like walls; therefore, it more accurately reflects functional proximity in high-risk environments for close contact: inside buildings, in vehicles and airplanes, and in underground transit,” wrote the research team at Covid Watch in a whitepaper.

They’ll have the cooperation of Google and Apple, the companies behind the two largest mobile platforms in the world, who are planning on releasing an API next month that will allow such Bluetooth-based apps to easily access both the iOS and Android platforms. It’ll ensure that two people who have different contact tracing apps downloaded, and who happen to cross paths, can still receive alerts if one of them happens to test positive.

The end goal, what both tech giants call “Phase II”, will eliminate the need for an app at all. Instead, people who opt in will be able to receive alerts automatically on their phone. It’s a move that would unleash Bluetooth contact tracing on an estimated 3 billion smartphones.

Critics argue that Bluetooth is also a flawed technology, and could deliver false positives or be vulnerable to hacking. Another barrier is adoption. How useful can digital contact tracing be if only a fraction of the population has the app installed? Only one in five people in Singapore have downloaded the Trace Together app so far—and researchers estimate that at least 60% of a country’s population needs to have a contact tracing app installed in order for it to be effective.

“Even the most-sophisticated digital tracing app won’t be of much help if smart phone users don’t download it. Without widespread installation, the apps are unable to gather enough data to enable effective digital tracing,” noted NIH Director Dr. Francis Collins in a blog post.

Which is why it’s no surprise that technologists behind Safe Paths, Covid Watch, and the PEPP-PT platform have all welcomed Google and Apple’s intervention, and plan on using their API. The involvement of the two tech giants will mean that most of the world’s smartphones will automatically be set up for digital contact tracing. NHS has said it plans to integrate Google and Apple’s API in its contact tracing app in the UK. Chris Boos of PEPP-PT told Reuters that it would “shorten the path to deployment” for digital contract tracing. Covid Watch Executive Director Tina White called the partnership a “game-changer.”

Google and Apple’s involvement will also lend digital contact tracing an air of legitimacy. The tech giants have agreed to only release their API to government agencies and public health authorities. State and local governments will work with platforms like Safe Paths, Covid Watch, and Seattle’s CoEpi to release regional version of the apps. That way, the market won’t be saturated with third-party contact tracing apps.

Ramesh Raskar, an associate professor at MIT Media Lab who leads the team behind Safe Path, also applauded the tech giant’s involvement. But he also cautioned that contact tracing would only be a small part of a wider set of digital solutions that public health officials needed to build. “So it’s important not to get our hopes too high,” wrote Raskar in an email to Quartz.

Beyond contact tracing, other groups are diving into efforts like building apps that will verify a person’s healthy status and generate immunity certificates—a concept with its own set of limitations. “Contact tracing is just a tiny part of the public health solution we need to build,” wrote Raskar.