[techcode]

I'm not so sure about always "stay indoors" part - in particular in case the dams leak and half of the country is about to be under water.

I guess depends on the height of your house - though in quite a few places even rooftop might be below or close to sea level.

[jacquesm]

Those are pretty far down on the likelihood scale, though we have had instances of that, especially near river dikes in the last couple of years. We do not have a lot of dams here.

The more likely cause for such an alarm is chemical pollution from either an accidental release or a fire. Their old use was for air raids but those are even more unlikely (at the moment, of course this can change).

[sverhagen]

The actual instruction from the government is:

* Go inside

* Close doors and windows

* Listen to the emergency channel

* Know when it is safe to go outside again

Sirens are sunsetting, but still operational until 2020.