The Swiss government maintains a network of around 7,200 sirens across the country as a public warning system that would be used in case of a national emergency. That could mean a natural disaster such as major flooding, or an imminent threat to or breakdown of a nuclear power plant.
Why this system?
The sirens were originally established to warn of bomb threat during World War Two. In particular Switzerland feared that its dams could be bombed in the manner that Germany's Möhne, Eder and Sorpe dams were bombed by the allies in 1943 (as recounted in the famous 1955 film The Dam Busters). The system endured through the Cold War when paranoid Switzerland feared being caught in the crossfire of a nuclear attack, and has been kept ever since.
What do they sound like?
There are two types of warning sirens. The first, indicating general disaster, is a continuous oscillating siren lasting around a minute. The second, used to warn people who live beneath dams of impending water-related catastrophe, is a series of 12 bursts of 20 seconds each at ten-second intervals. You can hear samples here.
When are they tested?
On the first Wednesday of February every year. The general alarm will be tested at 1.30pm for around half an hour. The water alarm test follows at 2.15pm in applicable areas.
Although the testing of the sirens is widely publicized on television and radio prior to the day (including with this tongue-in-cheek advert, below), it can still be a bit of a shock to newcomers to the country. Just take the lead of the Swiss – ignore it and carry on.
What happens if the alarms go off for real?
If you ever hear the alarm and it's NOT the first Wednesday in February, we're in trouble. In the case of the general alarm, the government's Office for the Protection of the Population (FOCP) advises that you listen to the radio, follow instructions and tell your neighbours to do the same. If you live below a dam and you hear the water alarm, there's no time to wait for instructions – just run like hell.
Has it ever been used?
The water alarm has thankfully never had to be used, however the general alarm has been deployed on occasions, including in 2007 when the river Aare in Bern rose to dangerous levels.
It's not very 21st century...
No, and indeed the government is currently developing a more up-to-date system, a smartphone app that would send a push notification in case of disaster or terrorism.
The Alertswiss system is already in use but a new, more sophisticated version should be ready by the end of this year and will be rolled out across the country in 2018.