How do COVID-19 tracing apps work?

With many of us in lockdown, governments across the world have been racing to find ways to ease restrictions without putting public safety at risk. One possible solution many governments have supported is a contact-tracing app, which can enable digital contact-tracing on a large scale. These apps are designed to let people know if they have been in close contact with someone who later is tested positive for Covid-19.

The hope is that with a large proportion of the population using such apps, governments will be able to pinpoint exactly who needs to be in quarantine and who doesn’t, making it key to easing up social distancing measures. The primary purpose is to alert people of the need to self-isolate faster than traditional methods have allowed in the past.

There have already been numerous trials of such apps across the world. In Singapore, for example, a contact-tracing app called TraceTogether has been rolled out by the government and has been downloaded over 800,000 times since March 20th 2020 in the hopes of creating a ‘community-driven’ response to the virus.

The way these apps will work will vary according to country, however they will use the same basic principles that we have outline below.

  • Users download the app and keep it on them at all times when outdoors.
  • The app then runs in the background of the phone, periodically sensing when another phone with the app comes into range via Bluetooth and how far away the two devices are from each other.
  • The app will anonymously log details of the other phone for a specified number of days.
  • If a user develops flu-like symptoms, they report these in the app. They will be asked a series of clinical questions.
  • The answers will then be analysed by an artificial intelligence (AI) programme. If the AI decides the symptoms meet a threshold for Covid-19, that person should self-isolate for 14 days.
  • The AI then analyses contacts the symptomatic person has logged in the app to decide the potential risk of infection for each. People deemed to have had ‘high risk’ contact with someone reporting Covid-19 symptoms will then be sent an alert advising that they self-isolate for 14 days in case they have contracted the disease. Those contacted won’t know the identity of the person who may have passed on coronavirus.

Centralised vs Decentralised

With a centralised tracing approach, the contact-matching happens on a remote, encrypted computer server. Public health bodies are also given access to this anonymous data, to see where hotspots of the infection are breaking out.

However, it is important to state that as the data collected is anonymous, those people contacted won’t know who may have passed on coronavirus, protecting their identity.

By contrast, the decentralised version carries out the process on the phones themselves. This means there is no central database that could be used to re-identify individuals and reveal with whom they had had spent time as the data will not exist.

What about Apple and Google?

Countries that are using Apple and Google to develop tracing apps differ slightly even though they use a decentralised approach. These companies are offering a piece of technology (an application programming interface or API) that will help turn all iPhones and all Android phones into contact tracing devices, directly integrating the technology into their operating systems to reach more people. Put simply, the companies themselves are not developing apps but are supporting developers who do wish to do so.

They are helping by:

  • Giving information about different devices’ Bluetooth power levels, to help developers better estimate how far two handsets are from each other
  • Letting developers decide for themselves how close together phones should be and for how long to trigger a ‘meeting’
  • Preventing the phones from logging any meeting as having lasted longer than 30 minutes
  • Encrypting data about the transmission power of the phones, to prevent anyone retrospectively using the logs to reveal what models had been involved
  • Changing to a different encryption algorithm to reduce the toll on battery life

This system is also interoperable, meaning even if people from different countries, states, or with different devices have different contact tracing apps, they will be alerted to exposure.

We hope this was useful in helping you decide if you want to download a contract tracing app. If you have any questions, please leave them in the comment section below and we will reply.

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