I don’t think they are as such. But it is my understanding that there is stock ready and regularly replenished ready to be deployed. It’s also a citizen responsibility to be ready. I think it’s not mandatory to build them anymore (stopped in 2014). But the amount of places in shelter is monitored and more will be built is population keeps growing this fast. 

https://www.babs.admin.ch/en/shelter 

 Sirens are tested each year. Kids learn from a young age what to do if they hear them. 

 As long as they are stocked for at least 2 weeks  🙌 

 Don’t forget some potassium iodide 😉