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Guide · GUIDE 02

Behaviour in siren alarm

Last reviewed on 05.07.2026

The general alarm is a regularly ascending and descending howl lasting one minute. It means: possible danger – listen to the radio (e.g. SRF 1), open the Alertswiss app or alert.swiss and follow the authorities' instructions. The water alarm (only below dams) consists of twelve deep continuous tones and means: leave the area immediately, seek higher ground. The annual siren test is on the first Wednesday in February from 13:30.

Switzerland has around 7,200 sirens (about 5,000 stationary and around 2,200 mobile). They have two signals: the general alarm – a regularly ascending and descending howl lasting one minute – means «possible danger, get information now»: turn on the radio (e.g. SRF 1), consult the Alertswiss app and alert.swiss and follow the authorities' instructions. The water alarm only sounds in the area below dams; it requires you to leave the endangered area immediately and seek higher ground. Sirens are tested every year on the first Wednesday in February from 13:30 – no action is required then.

What does the siren alarm in Switzerland mean?

The general alarm does not say what has happened – it only says: there may be danger, get information now. The specific instruction (stay indoors, close windows and doors, leave the area or prepare iodine tablets) comes afterwards via radio and Alertswiss.

There are two different signals: the general alarm and – only in the area below dams – the water alarm. Confusing them can be dangerous: in a water alarm, there is no time to wait for information first; immediate action counts.

For the all-clear («danger over»), there is no separate siren signal. The end of an alarm and return to normal are announced via radio and Alertswiss – not by a siren sound. If you have not heard an all-clear, follow the last given instructions.

The two signals in detail

  1. General alarm: regularly ascending and descending howl lasting one minute; it is repeated within five minutes. Meaning: get information immediately.
  2. Water alarm: twelve deep continuous tones of 20 seconds each at 10-second intervals. It sounds exclusively in the hazard area below dams. Meaning: leave the endangered area immediately (and according to local leaflet seek higher ground).
  3. The alarm tones are broadcast during the annual siren test for practice. Outside of the test, a signal always means a real reason to get information or take action.
Switzerland siren signals – tone, meaning, immediate action
Signal Tone pattern Meaning Immediate action
General alarm regularly ascending/descending howl, 1 minute (repeated within 5 min) possible danger – get information Listen to radio (e.g. SRF 1), Alertswiss/alert.swiss, follow instructions
Water alarm 12 deep continuous tones of 20 s, 10 s intervals (only below dams) acute flood risk Leave area immediately, seek higher ground
All-clear no separate siren signal danger over End announced via radio/Alertswiss; until then follow instructions
Siren test General alarm from 13:30 (below dams water alarm from 14:00) annual function check no measures needed – 1st Wednesday in February

Source: FOCP / Alertswiss. Switzerland has two siren signals (general alarm, water alarm) and no separate all-clear signal – the all-clear is announced via radio and Alertswiss.

What should I do when the siren sounds?

  1. Turn on the radio: SRF 1 or a regional/local radio (FM/DAB+)
  2. Open the Alertswiss app or alert.swiss and read the current message
  3. Follow the authorities' instructions (e.g. stay indoors, close windows and doors)
  4. Inform neighbours and people around you – not everyone hears or understands the siren
  5. Keep the telephone network free for emergency calls – do not make unnecessary calls
  6. Only in case of water alarm: do not wait for information, leave the area immediately and seek higher ground

The siren test in February

Once a year, on the first Wednesday in February, the federal government, cantons and municipalities test the sirens. The general alarm is triggered nationwide from 13:30. In the area below dams, the water alarm is also tested – from 14:00 (until 16:30 at the latest).

During the test, no action is necessary – no cause for alarm, no measures. The test ensures that the sirens work in case of emergency.

The test is a good opportunity to check your own preparedness: is the Alertswiss app installed and are push notifications activated? Does a battery-independent radio work (battery/crank)? Are spare batteries and a charged power bank available? Remember the date so you do not confuse the test with a real alarm.

Heard the siren but no information – what to do?

An alarm outside of the February test is always a real incident. If you hear the siren but cannot find information, it is usually because the information is still coming via radio and Alertswiss or your usual channel is temporarily unavailable. Stay calm and work through the channels in order.

Important: during a power outage, mobile antennas can fail. A battery-independent reception path – a battery or crank radio – is then the most reliable way to get information. FM penetrates cellars and shelters better than DAB+.

  1. Turn on the radio – first SRF 1, then a local/regional radio (try FM and DAB+)
  2. Check the Alertswiss app and alert.swiss (federal government website)
  3. Use a battery-independent battery/crank radio if power or mobile network fails
  4. Do not go outside to «check»; do not clog the telephone network with calls
  5. Wait for the all-clear via radio/Alertswiss; until then follow the last instructions

What you should have ready

To get information immediately in case of alarm, a battery-independent reception path is worthwhile – mobile antennas and the internet can fail during a power outage.

  1. Battery or crank radio (FM/DAB+) with spare batteries
  2. Charged power bank for your smartphone
  3. Alertswiss app installed and push notifications enabled
  4. Know which broadcasters provide information in your region (SRF 1, local/regional radio)

Common mistakes / misconceptions

  1. Ignoring the siren or going outside to «check» instead of getting information
  2. Immediately calling and clogging the network for emergency calls
  3. Confusing general alarm and water alarm – in a water alarm immediate action counts
  4. Waiting for an «all-clear siren» – it does not exist; the all-clear only comes via radio/app
  5. Confusing the February siren test with a real alarm (know the date!)
  6. Relying only on the smartphone – mobile network can fail during a power outage

Frequently asked questions

What does the siren sound mean in Switzerland?

The general alarm is a regularly ascending and descending howl lasting one minute. It means: possible danger – now turn on the radio (e.g. SRF 1), open the Alertswiss app or alert.swiss and follow the authorities' instructions.

What is the difference between general alarm and water alarm?

The general alarm is an ascending/descending howl lasting one minute and means «get information». The water alarm consists of twelve deep continuous tones (20 seconds each, 10-second intervals), sounds only in the area below dams and means: leave the area immediately and seek higher ground – without waiting for further information.

When are the sirens tested?

Every year on the first Wednesday in February. The general alarm is triggered from 13:30; in the area below dams the water alarm is also tested from 14:00. During the test, no measures are necessary.

What must I do in case of water alarm?

Do not wait for information: leave the endangered area immediately and seek higher ground. The water alarm sounds only in the hazard area below dams and warns of sudden flooding.

I heard the siren but cannot find any information – what now?

Stay calm and check the channels in order: SRF 1, then local/regional radio (FM and DAB+), then the Alertswiss app and alert.swiss. In case of power outage, use a battery-independent battery or crank radio. Do not go outside to check and do not clog the telephone network with calls.

Is there an alarm app, and where does the all-clear come from?

Yes: Alertswiss is the official warning app of the federal government (also as website alert.swiss), free for iOS and Android. Behaviour instructions and all-clear run via radio and Alertswiss – there is no separate siren all-clear signal.

Why shouldn't I rely only on my smartphone during siren alarm?

During a power outage, mobile phone antennas may fail and mobile networks as well as the internet can break down. A battery or crank-powered radio (FM/DAB+) is then the most reliable way to get information. FM also penetrates cellars and shelters better than DAB+. Keep spare batteries and a fully charged power bank ready.

How many sirens are there in Switzerland?

Switzerland has around 7,200 sirens – approximately 5,000 stationary and around 2,200 mobile. They have two signals: the general alarm (a regularly ascending and descending howl lasting one minute) and the water alarm in the area below dams. They are tested annually on the first Wednesday in February.

Official sources