Can Bluetooth Contact Tracing Apps Really Help Fight Pandemics?


h to automate contact tracing, letting you know if you’ve crossed paths with someone who has tested positive for COVID-19.


  • New apps from the likes of MITGoogle, and Apple rely on Bluetooth to automate the contact-tracing process, which health care professionals use to notify people who may have come into contact with a COVID-19 patient.
  • The idea is to proactively trace individuals’ movements so that if the person does eventually test positive, there’s a definitive way to track their previous whereabouts–and who else was nearby at the time.
  • While sound in theory, these apps will only work if a broad swath of the population adopts them.

After a patient tests positive for COVID-19, health care professionals begin to notify individuals who may have crossed paths with that person. This is both for their own safety and to ensure that those infected self-quarantine to quell the spread.

But a March 31 paper published in Science details how the break-neck pace of this pandemic cannot be tracked through traditional methods (often involving painstaking in-person interviews). So the experts turn to technology by recommending digital contact tracing as a way to prevent widespread lockdowns.CONTACT-TRACINGThis MIT App Tracks the Spread of Coronavirus

“A contact-tracing app which builds a memory of proximity contacts and immediately notifies contacts of positive cases can achieve epidemic control if used by enough people,” they write. “By targeting recommendations to only those at risk, epidemics could be contained without need for mass quarantines (‘lock-downs’) that are harmful to society.”

Countless examples of this sort of technology are already in development, including a joint Google-Apple venture that the two tech giants announced April 10, and an academic effort called PACT (Private Automatic Contact Tracing). Led by the MIT and in partnership with a consortium of universities and public health organizations, PACT researchers have banded together to build a Bluetooth protocol meant to track users’ location and COVID-19 status.ADVERTISEMENT – CONTINUE READING BELOW



Their approach relies on Bluetooth communications in smartphones “as a proxy for inter-person distance measurement.” In other words, Bluetooth signals in your smartphone can determine how close you’ve come to another person by detecting their Bluetooth transmissions. As individuals test positive, the app will send exposure notifications to all smartphone users who have come into close contact with the patient across the span of the prior two weeks, while they were infectious.

Importantly, this can be done without revealing any private information about the individuals using the app. Not the government, health care providers, or cellular providers.

But it has one big flaw—everyone needs to use it.

Preserving Privacy

According to a PACT technical paper, each person’s smartphone emits anonymous, random “chirps,” on a continual basis. Chirps cannot be linked to the device or the owner and are “rotated” every few minutes so that bad actors cannot use them to track the device. Each device keeps a log of the chirps it transmits and the chirps it’s received. This is all done through the Bluetooth Low Energy (BLE) protocol, which is used to wirelessly connect your devices.

“I keep track of what I’ve broadcasted, and you keep track of what you’ve heard, and this will allow us to tell if someone was in close proximity to an infected person,” Ron Rivest, MIT Institute Professor and principal investigator of the project, said in a prepared statement. “But for these broadcasts, we’re using cryptographic techniques to generate random, rotating numbers that are not just anonymous, but pseudonymous, constantly changing their ‘ID,’ and that can’t be traced back to an individual.”



PACT’s protocol not only collects data on the proximity between two devices, but also accounts for the duration of time two devices have been near one another. Other metadata, like the specific location, can help determine if a person may be in dangerous contact with another: a restaurant, the researchers note, is a far more risky location than a bike path. That metadata isn’t included in the chirp, but is logged locally in a phone’s metadata and can be associated with a received chirp in its contact log.

The researchers modeled their work on Apple’s Find My app, used to locate lost or stolen devices. “If my phone is lost, it can start broadcasting a Bluetooth signal that’s just a random number; it’s like being in the middle of the ocean and waving a light,” Marc Zissman, the associate head of MIT Lincoln Laboratory’s Cyber Security and Information Science Division, said in a prepared statement.

If someone walks by with Bluetooth enabled, their phone doesn’t know anything about me; it will just tell Apple, ‘Hey, I saw this light.'”

In its final iteration, the PACT project will take the form of a smartphone app. When an individual tests positive, they upload all of the chirps that their phone has sent out over the last two weeks. Those chirps are stored in a separate database for positive COVID-19 cases to ensure the person’s device is not associated with their COVID-19 status.ADVERTISEMENT – CONTINUE READING BELOW

PACT states that to keep the integrity of the data private, an authorized medical professional should facilitate the data entry. “The chirps corresponding to Bob’s device are essentially just random numbers that cannot be linked to any information identifying Bob. In fact, they cannot even be linked to each other,” according to the report.

But Will the App Work?

According to Farzad Mostashari, the former national coordinator for health information technology at the U.S. Department of Health and Human Services, contact tracing has a few inherent problems.Farzad Mostashari@Farzad_MD

1/ How can we safely reopen our cities?

You’ll see many plans that rely on invigorated contact tracing to “reclaim containment” 💯

Some argue for use of apps to track our close contacts-> instant digital contact tracing

Should we be pushing for this? …Quantifying SARS-CoV-2 transmission suggests epidemic control with digital contact tracingThe newly emergent human virus SARS-CoV-2 is resulting in high fatality rates and incapacitated health systems. Preventing further transmission is a priority. We analyzed key parameters of epidemic…science.sciencemag.org159Twitter Ads info and privacy82 people are talking about this

“I think the interest in this is partly just because there are so many brilliant technologists in Silicon Valley and elsewhere who are looking at the unfolding pandemic helplessly, and they want to help,” Mostashari writes. “I applaud this, but we need to consider public health utility and privacy.”

For the app to be useful, the rate of adoption has to be extremely strong. As you might expect, there is a positive correlation between the number of people who use a contact-tracing app and the overall effectiveness of the app. As more people use it, the more worthwhile it is. But Mostashari notes that even if 1/3 of the population downloads and uses a contact-tracing app, it will still only cover about nine percent of close interactions.



For digital contact-tracing to work, a protocol like the one under development at MIT would have to be pushed out through an update on iOS and Android operating systems. An app is not compulsory and does not necessarily lead to high adoption rates.

“If such a tool exists to trace close contacts of most Americans, what are the chances that they will not be used for law enforcement, by intelligence agencies, or hacked?” Mostashari writes.


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