The Swiss government maintains a network of around 7,200 sirens across the country as a public warning system for use in case of a national emergency, such as a natural disaster or breakdown of a nuclear power plant. The sirens were originally established to warn of bomb threat during WWII. They were also relied upon throughout the Cold War when Switzerland feared being caught in the crossfire of a nuclear attack, and has been kept ever since.
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.
They are tested on the first Wednesday of February each 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.
However, if you 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!
The government is developing a more up-to-date system - a smartphone app that would activate 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.