On Thursday morning there will be tests for the cell broadcasting system, sirens and other public warning system. At 11am your smartphone will make insanely loud noises! All clear signals will be at 11:45am.
Unfortunately there seems to be no english website for it, here is the german site: https://www.bbk.bund.de/DE/Warnung-Vorsorge/Bundesweiter-Warntag/bundesweiter-warntag_node.html
by siantre