Short answer. Luxembourg warns the public through LU-Alert: a free app, location-based SMS, Cell Broadcast, government websites, the media and social media 12. Outdoor sirens are currently used only for a nuclear alert and use three signals 14. Sirens and the other channels are tested on the first Monday of every month at around midday 2.
Information verified on 20 October 2026.
Which channels does LU-Alert use?
| Channel | Setup needed? |
|---|---|
| LU-Alert mobile app (iOS and Android, free) 1 | Install the app |
| Location-based SMS (LB-SMS) 2 | None |
| Cell Broadcast (CB) 2 | None, except the "LU-Alert Test" level, which is off by default |
| Government websites: lu-alert.lu, meteolux.lu, inondations.lu, data.public.lu, and infocrise.lu 15 | None |
| Press (radio, TV, websites, apps) and social media 1 | None |
| Sirens, currently only for a nuclear alert 1 | None |
Location-based SMS and Cell Broadcast reach phones in the affected area without registration 2. For why a radio matters when networks fail, see Which emergency radio should you choose?.
What do the sirens mean?
The government brochure on nuclear alerts describes these signals 4:
| Signal | Pattern | What to do |
|---|---|---|
| Standby (preliminary alarm) | Warbling tone lasting one minute | A radioactive release is possible but not imminent: stay informed, fetch children from crèche or daycare, get iodine tablets ready, avoid travel, cover the vegetable garden |
| Nuclear alarm | Warbling tone lasting one minute, interrupted by two pauses of 12 seconds each | A release is imminent: take shelter in a solid building, close doors, windows and shutters, switch off ventilation, follow the media and infocrise.lu |
| All clear (end of alarm) | Continuous tone lasting one minute | Dispersion of the radioactive release has ended |
| Fire alarm (not a public warning) | Continuous tone lasting three minutes | Fire-service call-out, distinct from the nuclear signals |
Sirens are triggered by region, municipality or locality, only in zones potentially under threat, not automatically nationwide 14. What to do once sheltered is on Public shelters in Luxembourg; tablets are covered on Iodine tablets in Luxembourg.
When are the tests?
On the first Monday of every month, at around midday 2. The test covers the sirens, Cell Broadcast, LB-SMS, the app and lu-alert.lu 2. If you hear the sirens at that time, it is most likely the scheduled test.
What alert levels does LU-Alert use?
The levels approved by the Government Council in July 2024 are 3:
- D: imminent danger, immediate action required.
- N1 red, N2 orange, N3 yellow.
- A: missing person or kidnapping.
- I: information.
- T: test.
For general advice on reacting to a warning, see What to do when an air-raid or emergency siren sounds.
Frequently asked questions
Do I need to register to get LU-Alert messages?
No. Location-based SMS and Cell Broadcast need no setup 2. The free app is optional 1.
Why did my phone not show the test alert?
On Cell Broadcast, the "LU-Alert Test" level is off by default 2.
Are sirens used for floods or storms?
Not at present. Sirens are currently used only in the event of a nuclear alert 1.
How do I tell the nuclear alarm from a fire siren?
The nuclear alarm is a one-minute warbling tone with two 12-second pauses; the fire-service call-out is a continuous tone lasting three minutes 4.
Sources
- LU-Alert (Government of Luxembourg) — What warning channels are used to transmit warning and information messages to the population? — https://lu-alert.lu/en/all-about-lu-alert/warning-channels.html (accessed 2026-10-20)
- LU-Alert (Government of Luxembourg) — What is the testing strategy for the "LU-Alert" warning and information system? — https://lu-alert.lu/en/all-about-lu-alert/testing-strategy.html (accessed 2026-10-20)
- LU-Alert (Government of Luxembourg) — What alert levels are used in the "LU-Alert" system? — https://lu-alert.lu/en/all-about-lu-alert/alert-levels-and-categories.html (accessed 2026-10-20)
- Information and Press Service of the Luxembourg Government, with the Ministry of Home Affairs, Health Directorate, Rescue Services Agency and HCPN — What to do in the event of a nuclear alert? — https://infocrise.public.lu/dam-assets/publications/urgence-nucl%C3%A9aire/BROCHURE-CATTENOM-WHAT-TO-DO-IN-THE-EVENT-OF-A-NUCLEAR-ALERT.pdf (accessed 2026-10-20)
- infocrise.lu (Government of Luxembourg) — Taking shelter — https://infocrise.public.lu/en/accident-nucleaire/gestes-protection/mise-a-l-abri.html (accessed 2026-10-20)
Turn this into action
Your plan for Luxembourg, worked out for your household.
- Water, food and equipment counted for each person and pet
- The nuclear plants and zones around your home
- Phaenyx Safe: one tap to tell your people you are safe
Sources
- LU-Alert (Government of Luxembourg) · What warning channels are used to transmit warning and information messages to the population? checked 2026-10-20
- LU-Alert (Government of Luxembourg) · What is the testing strategy for the "LU-Alert" warning and information system? checked 2026-10-20
- LU-Alert (Government of Luxembourg) · What alert levels are used in the "LU-Alert" system? checked 2026-10-20
- Information and Press Service of the Luxembourg Government, with the Ministry of Home Affairs, Health Directorate, Rescue Services Agency and HCPN · What to do in the event of a nuclear alert? checked 2026-10-20
- infocrise.lu (Government of Luxembourg) · Taking shelter checked 2026-10-20