At exactly 11:00 a.m. on Thursday, September 11, 2025, sirens will sound across Germany and loud alerts will appear on millions of smartphones.
The so-called Warntag, or nationwide warning day, is a coordinated test by federal, state, and local authorities to measure how effectively Germany’s emergency alert system works in practice.
Organized by the Federal Office of Civil Protection and Disaster Assistance (BBK), the test sends a trial alert through the Modular Warning System (MoWaS) to broadcasters, warning apps such as NINA and KATWARN, and to the cell broadcast network used by mobile operators.
The goal is simple: to ensure that in the event of a flood, power outage, terror attack, or other large-scale emergency, the public can be warned quickly and reliably.
How the test unfolds
At 11:00 a.m., warning signals are transmitted nationwide.
Sirens, radio and television messages, and push notifications on mobile phones are triggered simultaneously.
Municipalities may also use loudspeaker vehicles for public announcements.
Around 11:45 a.m., an official all-clear signal follows.
For clarity, an ascending and descending siren tone indicates “population warning,” while a steady tone signals “all-clear.”
Knowing these distinctions can be crucial in a real emergency.
Why a nationwide test is necessary
The warning day was first introduced in 2020, but its debut was plagued by technical failures—many people received alerts late or not at all.
The catastrophic Ahr Valley floods in 2021 further highlighted how vital fast communication is when disaster strikes.
Since then, the system has been steadily upgraded. According to BBK, 54% of the population received alerts via cell broadcast in 2022.
By 2023, this had increased to 72%, and in 2024, an estimated 96% of residents were reached through at least one channel.
Today, Warntag is a fixed annual exercise, held on the second Thursday of every September.
Smartphone settings: what to check in advance
Authorities recommend a quick check of device settings before the test:
- Android phones: Cell Broadcast is supported from Android 11 onwards.
- iPhones: The feature works from iOS 16.1.
Ensure notifications are not disabled, and the phone is not in “Do Not Disturb” mode.
For extra coverage, install warning apps such as NINA, which also provide local alerts.
International comparisons
Germany is not alone in testing its warning systems. In the United States, Wireless Emergency Alerts (WEA) reach mobile phones directly.
The UK has its National Alert System. While many countries rely mainly on cell broadcast, Germany is expanding its use of sirens—a traditional but highly effective method, especially for those without smartphones.
Conclusion
Warntag is not a real emergency but a nationwide rehearsal designed to familiarize people with warning tones and ensure systems function as intended.
By checking their phones and understanding the siren signals, residents can be better prepared for situations in which every minute matters.
