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Covid-19 contact tracing APPs are used to detect and warn users who have been in close contact with Coronavirus patients. Most of them are Bluetooth based apps, scanning for Bluetooth Low Energy beacons in proximity to one another. Each beacon is characterized by a UID (Unique IDentifier), a 32-byte hex number which can be used to unambiguously identify the transmitting device.
The contact information can be uploaded to a cloud database, allowing the transmitting device to be located at a later point of time if needed. Most of the Covid-19 contact tracing app collect anonymous data, meaning that the user information is replaced by the beacon UID. During the registration of the Bluetooth based app, the UID of the beacon is stored together with the means to contact the user in case of need.
Bluetooth Low Energy technology
As we mentioned before, most of the covid-19 tracking apps are based in Bluetooth Low Energy technology. Bluetooth Low Energy (BLE or BT-LE, depending on the source) is the name given to the version 4.x of the Bluetooth standard (current latest version available is 5.2).
Traditional Bluetooth was mainly developed for transmitting files and data between devices in close proximity. Thus, the main requirements for Bluetooth were high data rates and throughput, while other aspects such as battery life or energy consumption were not very important.
Bluetooth Low Energy targets other type of applications that do not require maybe high data rates, but they required to send small pieces of information in a periodical way. The energy consumption is critical, since this technology is aimed at devices that may be installed in remote locations and the battery consumption shall be low.
Bluetooth Low Energy beacons
BLE is based in the transmission of small data packages called beacons. BLE beacons have a unique identifier and contain small amounts of information. They are transmitted periodically (e.g. each 100 ms) on one of the Bluetooth advertising channels.
There are multiple beacon formats from different companies. Some of the most popular are the iBeacon, the AltBeacon and the Eddystone. Depending on the application, the information on the beacon can change. For example, a vending machine could transmit a periodical beacon indicating how many soda cans it has left. That way the vending company could optimize the loading process.
Typical Bluetooth Low Energy beacons used for positioning applications contain the UID and potentially some kind of hierarchical organization of the Bluetooth network. For example, in a shopping mall using BLE for location based services, each beacon could be labeled based on the floor and section.
Covid-19 contact tracing apps
Video Tutorial
Check our video tutorial on Covid-19 tracking apps based on Bluetooth Low Energy. By clicking on the image, the video will open in a separate tab.
Example
Now that we know the basic on Bluetooth Low Energy, how can this principle be applied to the Covid-19 contact tracing apps? Let’s check that with the example in the image.
In the example, User 1, 2 and 3 have installed a Covid-19 contact tracing app. Their smartphones are constantly transmitting, with a certain periodicity, a unique Bluetooth Low Energy beacon. There is no other device in the world transmitting this same signal. The company that created the Covid-19 contact tracing app knows to which device is the signal registered and how to contact this device at every time.
Let’s say at a certain point in time, all three users were close to each other for a while. This is the proximity area shown in the figure. Of course at that time, none of the users has been diagnosed with Coronavirus yet, but they could still be infected without knowing. The Covid-19 tracking app installed in their smartphones receives the bluetooth low energy beacon from the other two and stores it. This information is also sent to the anonymous contact database, where it is kept. Now the system officially knows that User 1, User 2 and User 3 (or rather their corresponding beacons) have been in contact.
After a while, User 1 starts showing Symptoms of Coronavirus and contacts the health care providers. He is finally diagnosed. What happens next? The authorities, in collaboration with the Covid-19 tracking app owner, identify who has been in contact with User 1 in the last few days (according to current scientific research, somewhere between two weeks and one month). The anonymous contact database retrieves the information that User 2 and User 3 have been in contact with User 1, so they could be infected as well. The authorities should now contact them with further instructions such as stay in quarantine, or he / she will be tested or whatever the protocol is in the corresponding country.
If User 2 or User 3 are tested and the sample confirms the Coronavirus disease, their contact will be notified as well and so on.
Flaws of Covid-19 tracking apps
These Bluetooth based apps rely on crowd-sourcing to obtain the necessary contact tracing information. Crowd-sourcing algorithms need a high number of participants (a big crowd :)) to function properly. For Covid-19 contact tracing apps to be effective they need to be installed and actively used by a large sector of the population.
As we have seen in our previous article, Singapore, the first country to introduce such an app, only managed to get about 15% of the population to register and use it. Other countries such as UK and Australia are aiming for 50% of the population to use their apps. Let’s see if they reach these numbers.
Not everyone has a smartphone and the technical knowledge to install and use apps. Especially the elderly, the sector most affected by Coronavirus, may struggle to use the Bluetooth low energy technology. Furthermore, for the apps to be effective, the corresponding user needs to carry the smartphone with him or her all the time. It does not help if a person leaves the smartphone at home to go running, for example.
There are of course as well privacy concerns, and the fact that their government or a private corporation can track users worries a sector of the population. The collected data is supposed to be anonymized, but this could be reverted unintentionally or maliciously.
All-in-all, Covid-19 contact tracing apps can be a useful tool to help identifying the Coronavirus patients and stop the spreading of the global pandemic, if used properly. However, they cannot replace traditional methods such as manual contact tracing by the police and general preventive measurements.
They also require the population to be informed and aware on how the app works in order to be effective. We hope this post can also contribute towards that goal.
Read also
Our article about Covid-19 tracking apps and their adoption in different countries.
Liked this? Check our other tutorials in the tutorial page.
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