We have a similar system, previously known as Hesa Fredrik (a big signal horn in every town and city). Now, the public varning system consists of VMA (Viktigt meddelande till allmänheten) IPA and other systems. Once a month there is a outdoor test of the imortant public announcement system, on the first Monday at 3 PM I think. 

So if you are in the process of invading Sweden, do it at 3 o’clock. 

usagov:

The Federal Emergency Management Agency and the Federal Communications Commission will conduct the first nationwide test of the Emergency Alert System tomorrow, Wednesday, November 9 at 2:00 PM Eastern time. It will last 30 seconds.

You may hear a message on radio or television saying, “This is a…