Preparedness Nudging for Warning Apps? A Mixed-Method Study Investigating Popularity and Effects of Preparedness Alerts in Warning Apps

•Preparedness alerts increase number of taken preparedness measures.•Challenges mainly activation and relevance; less representational fidelity of alerts.•Rational-confrontational and social nudges deemed most adequate for warning apps.•Positive effect of rational-confrontational nudge on reported preparedness measures.•Positive evaluation of preparedness alerts increases motivation to use warning app.