An estimated 20-30 users have so far registered on the app that they've contracted coronavirus, Spiegel reported on Thursday.
And on Tuesday night, those who had been in contact with these people over a certain period of time will have received a corresponding warning message from the app.
App users who have received this notification can get in touch with their local health authorities and be tested for coronavirus free of charge.
However, it's not mandatory – authorities have no way of knowing who's been alerted. That's because the information is not collected centrally, but instead on users' smartphones to protect privacy.
The data is encrypted and automatically deleted after two weeks.
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The app was launched on June 16th, with authorities calling it a “big step” in the battle to control the spread of Covid-19.
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To calculate the risk of a person getting the virus, the app takes into account how long the contact with infected persons was, how much distance there was between them, and when exactly the infected persons tested positive.
The app can only display the estimated risk of infection, so anyone who gets a warning message is advised to get tested.
Now for the science part…
The app uses bluetooth to monitor which other smartphones using the app are in the vicinity and for how long.
If you come into contact with someone for around 15 minutes or more who also has the app, has tested positive for Covid-19 and submitted this information into the app, you'll receive the warning message.
No details, such as who tested positive or the location of where the person was, are disclosed.
Germany's app in the spotlight in UK
It came as British Prime Minister Boris Johnson was confronted over his claim that no country has a working contact-tracing app with news about Germany.
Labour leader Keir Starmer told Johnson that Germany's app launched last week and had 12 million downloads.
Boris Johnson confronted over claim no country has working coronavirus app pic.twitter.com/971qT9Voyy
— The Independent (@Independent) June 24, 2020