Corona warning app: the most important facts

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The federal government's corona tracing app is intended to help track chains of infection quickly and thus keep the corona pandemic in Germany under control. Here you can read how the app works, what the data security of the users is like and what the app can and cannot do.

How can the app help?

The app developed by SAP and Telekom on behalf of the federal government is intended to help detect chains of infection as quickly and comprehensively as possible. At the moment, health authorities have to do this in painstaking detail. This costs a lot of time in which unknowingly infected contacts can pass the virus on. There are also loopholes because anonymous encounters cannot be traced.

The corona tracing app therefore offers the following advantages:

• The app works quickly. Contact persons who have installed the app will be informed about contact with an infected person in the shortest possible time and can take precautionary measures for their part.
• The app also records anonymous encounters, for example on the bus, in a supermarket queue or while sunbathing. Normally, these contacts would not find out that there was a direct risk of infection.
• This also applies to forgotten contacts - like chatting with the neighbor in the stairwell.

New function: event registration

With the 2.0 update, the warning app offers a new function: it now includes the option of registering events. You can use this to check in at retail stores, events or private meetings using a QR code.

In this way, possible infection clusters are to be recognized and chains of infection are to be interrupted faster and more reliably. This data is also only saved locally on the mobile phone. They are automatically deleted after 16 days.

This distinguishes it from the privately developed Luca app, which many people already use, but which is often criticized for its data insecurity.

Digital vaccination certificate from summer

Another feature is to follow in summer 2021: the digital corona vaccination pass. With this certificate, users can prove that they are fully vaccinated. Even people who have recovered from corona disease can prove this with the app. In addition, it should display negative corona test results.

How does the app work?

The corona tracing app works via Bluetooth technology. For example, Bluetooth wirelessly links cell phones with speakers or headphones. In contrast to this "conventional" connection, the Corona warning app uses Bluetooth technology that consumes significantly less electricity (BLE = Bluetooth Low Energy). In this way, the mobile phone determines how close a person comes to another who has also installed the app. The duration of the encounter is also recorded.

Closer than two meters, longer than 15 minutes

A distance of less than two meters over a period of 15 minutes is considered a critical mark. Then an infection is considered possible.

The app also determines the signal strength and detects whether there was, for example, a wall between two people. Such a situation is not counted as a risk encounter.

"Digital handshake"

When people whose smartphones are equipped with the tracing app meet, the devices exchange certain identification numbers - a "digital handshake", so to speak, takes place.

Anonymous local storage

The contacts are only saved locally on the respective cell phone, anonymously. Every device randomly generates a new identification number (ID) every 20 minutes in order to further protect privacy. The location, movement profile or identity of the user are not recorded.

Deletion of the data after 14 days

After 14 days, when the incubation period for the disease ends, the contact is automatically deleted.

What happens if a user tests positive for Covid-19?

If a tracing app user reports a positive Covid-19 test, all temporary IDs that their mobile phone generated in the past 14 days are sent to a server. There they are available for all other users to compare.

The cell phones of all Corona app users check regularly, even several times a day after an update, whether their stored data matches that of those who tested positive on the server. In this case, users receive a warning that critical contact with an infected person has taken place. However, you will not find out when or where this happened, and certainly not who the infected person is. Conversely, the infected person does not find out who is being warned.

What can the app not do?

The Corona warning app is aimed at risky situations in which a droplet infection can occur. For a long time, this was considered the main route of transmission. It is now known, however, that most people become infected through floating microdroplets (aerosols) that contain viruses.

This transmission mainly takes place in closed, poorly ventilated rooms - over a distance of several meters. The app cannot recognize these risk situations, confirms the Robert Koch Institute (RKI) to

In addition, the app does not distinguish whether the people wore mouth and nose protection when they met. According to recent studies, wearing masks can significantly reduce the risk of infection for other people.

How reliably does the app work?

The app is not infallible. A key factor here is the Bluetooth measurement, which was not developed for such use. The strength of the signal varies from cell phone to cell phone. It also makes a difference whether you carry your mobile phone in your pocket or openly in your hand.

When asked by, the RKI explained that there were various test scenarios for this: standing in line, at a party or on public transport, among other things.

Misjudgments inevitable

There will always be situations in which the distance is misjudged during an encounter. If the rating is too low, there may be false-positive warnings - the contact person will then be warned even though the distance for a droplet infection was too great. In the opposite case, the contact person does not receive a warning, although the distance was closer.

The developers have not yet provided any information on how often such false reports could occur.

How safe is my data?

In contrast to Corona apps in other countries, movement profiles of the users, such as would be possible via GPS, are not recorded.

Decentralized approach

The German corona tracing app is also based on a decentralized approach. Anonymized contact data are stored on the respective smartphones. The contacts are also not checked on a central server, but on the smartphones themselves. This is to prevent the contact data from being hacked and accessed by unauthorized persons.

Code visible to everyone

In order to rule out security gaps as far as possible from the outset, the developers have published the entire programming code of the app so that it can be viewed and checked by everyone.

The Chaos Computer Club, a very critical advocate of data protection, now rates the security of the app as positive due to the decentralized data storage and after disclosure of the code.

Can the app be maliciously misused?

There could be a security hole in reporting a positive test result. It is feared that malicious people will abuse the function and report false positive test results in order to wreak havoc. Therefore, the test result needs to be verified when it is entered into the app. Ideally, this is done using a QR code that the laboratory sends to the person's mobile phone.

However, not all laboratories are equipped for this. Alternatively, the infected user can receive a TAN from the health department. There it is checked beforehand in the conversation whether the user is trustworthy.

Is the use of the app voluntary?

The Corona Tracing app is installed and used on a voluntary basis. It is not installed automatically, but must be actively downloaded. Users who have tested positively are also not obliged to feed the test result into the app. Anyone who receives a warning as an app user is also not obliged to take any measures - for example, to have themselves tested or to isolate themselves.

Nevertheless, some parties are demanding that it be stipulated by law that, for example, employers may not order the use of the app or that access to certain services and locations such as airports, restaurants or nursing homes may not be restricted to app users.

Who can use the app?

You currently need a smartphone with Bluetooth to use the app. This function must also always be switched on.

Apple provides the app for iPhones with operating system version iOS 13 or higher, Google for devices with Android 6 or higher operating system.

Critics complain that this excludes people who do not have a modern smartphone, including many older people who belong to the risk group. This could be solved using separate devices, for example appropriately equipped key fobs, which would have to be developed for this purpose.

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