When living in a foreign country the first thing you have to get used to are the new sounds. The first time I heard this I got a little panicky. I hear this every first monday of the month at noon. If I should hear this at anyother time I need to shut all windows and doors and turn on the radio or tv. This is used as a warning system for anything from an air raid to a disaster in a chemical plant. If there were a fire in a chemical plant and there was toxic gases coming out,this sound would go off and everyone knows that they need to get inside and follow the drill rules.