COVID 19 – How does a contact tracing app work?

As the death toll due to the COVID 19 continues to increase, countries around the world have been scrambling to source PPE for their medical personnel and researchers are going all hands on deck to find a cure and a vaccine. Despite having doubts on its efficiency, countries are trying their best to build a stock of hydroxychloroquine. And it’s not just governments, researchers, and healthcare professionals that are doing their best, some of the top tech companies in the world have been bringing forward their resources to fight the virus.

Contact tracing apps – the origins

Contact tracing apps are one of the innovative solutions that have recently come up in the fight against the coronavirus. The idea was piloted in China where the virus first originated. Alipay, a payment system from Alibaba, used a system of coloured QR codes to notify people who need to quarantine or isolate themselves. The users have to fill up a form, with information such as travel history, and information that may suggest they have the infection, such as a strong cough or high body temperature. The app will then generate a coloured QR code. People who got a red colour were asked to quarantine for 14 days, yellow colour indicated 7 days of quarantine and a green colour indicated that they were free to travel. The app was used in major checkpoints, and in some cases, entry to apartment buildings was also determined using the app. 

Why do we need a contact tracing app?

The idea behind a contact tracing app is to find the people who may have come in contact with an infected person. To contain an outbreak, isolating and quarantining people who are likely to be infected is a major step. While a nationwide lockdown helps, it is much more difficult to enforce, and even then the family members of an infected person may get infected. Generally, contact tracing is done by asking an infected person where they have visited, people they may have come in contact with and informing them. This system, while effective, has its drawbacks. Nobody remembers everyone they have come in contact with in the last two weeks. And if they have used public transport, or if they have just been out in public, it’s simply impossible to find out who they may have come in contact with. It is possible to ask everyone who has been to this location to isolate themselves, but that will be a huge number of people, and of course, many won’t listen unless there’s a fair degree of certainty that they have been exposed. 

This is where an app comes useful. The latest, and quite possibly the most successful effort is from a collaboration between Apple and Google. While the tech giants themselves won’t be building the app themselves, they are working on an application programming interface (API) that allows public health authorities to build that.

Here’s how a contact tracing app work

With the APIs, when two people (or rather two devices) come in close proximity to each other (within the range of Bluetooth), their devices exchange “keys” unique to the devices. In this way, each individual device will have a set of keys for each device it has come in proximity with. If a person contracts the disease, they will update their info on the app, which will be synced to a database. And all the devices that have come in contact with the infected person will receive a notification. 

When two people come within Bluetooth range, their smartphones exchange keys unique to their device

It’s basically like this. Imagine you’re taking down the list of everyone you come in contact with. And you’re checking the list of infected people every day, and you compare it with your list. If you find someone in common, you can isolate yourself and check for symptoms. 

But the process is completely automatic(except the part where you have to update if you get sick), faster, and more private. Since only keys linked to the smartphones are used, you remain anonymous, and while everyone who has come in contact with an infected person will get a notification, nobody can tell who they got it from. And the system will be platform independent, it doesn’t matter if one user has an Android phone and the other has an iOS device.

Added benefits

Apps like these can ease lockdown restrictions and allow things to get back to normal more easily and more quickly. In Britain, the health minister announced that the NHS will be rolling out a contact tracing app, and urged the public to download it. It is hoped that the app will give a better idea of people at risk, and slowly remove the lockdown restrictions. 


Of course with any technology that tracks people, there are questions about privacy. For example, when China deployed the app from Alibaba, there were widespread concerns about how the same technology may be used to spy on its citizens. 

It was a scandal when it came out that Google was tracking your location even when the location was turned off. And even with all the benefits it provides, I’m not comfortable having my location settings turned on. So, security researchers have more than enough concern about an app that more or less tracks every interaction a person had.

But the initiative from Apple and Google may be one of those rare instances where companies that live on data from consumers argue for more privacy. France wanted to ease the privacy restrictions on the app, demanding collection of much more comprehensive information about the patients. But Apple hasn’t backed down so far. And in the era of privacy laws and concerns, the public is already wary about apps that collect location data. So any wrong moves on the government or the public that has the public concerned about their privacy may affect any benefits that may come out of using such an app. 

Apple and Google expect to add the capabilities to iOS and Android phones respectively by Mid-May, so hopefully, that may help to ensure a smoother transition to normalcy as countries are starting to ease down on the restrictions. 

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