Now a days many are completely oblivious and have no clue although the government provides a handy guide to what you should keep [1] . Most have iodine pills at home as they are sent in the mail if you are close enough to a nuclear reactor. Everyone else can get them for free at the pharmacy.
In fact many don't know where their bomb shelter is, if it's not part of their home. Every home used to have a yellow plak which stated where the shelter is but because people are very mobile today the government will inform the public where they should shelter when an incident occurs. Also many of the bomb shelters are now used for other things such as storage. I remember as a kid when we bribed the inspector to come back later so we could clean out the shelter for inspection so we would not be fined. The shelters have active air filters and other requirements that were regularly inspected. At least you can now use them for storage and other things as long as you can clean it out in 24-48 hours.
Sirens are tested once a year and usually will freakout tourists which is entertaining to watch.
For anyone visiting or living in Switzerland I highly recommend downloading the Alert Swiss app [2] which will let you know what is going on like if you should close windows because of a chemical fire or if there is a siren test.
[1] https://www.bwl.admin.ch/bwl/en/home/themen/notvorrat.html