Who does or does not use the 'Corona-Warn-App' and why?

To slow the spread of SARS-CoV-2, the German government released the 'Corona-Warn-App', a smartphone application that warns users if they have come into contact with other users tested positive for SARS-CoV-2. Since using the 'Corona-Warn-App' is health-relevant behavior, it is essential to understand who is (and who is not) using it and why. In N = 1972 German adults, we found that non-users were on average older, female, healthier, in training and had low general trust in others. The most frequently named reasons by non-users were privacy concerns, doubts about the effectiveness of the app and lack of technical equipment.