Every year in Poland on the 1st of August at exactly 5pm all the emergency sirens (air raid sirens etc. call it whatever you want) are turned on simultaneously all around the country in remembrance of the 1945 Warsaw uprising (it started on the 1st of August 1945 at 5pm). Its also customary to stop for a minute and stand still or stop your car if it’s possible. Basically wherever you are in Poland on the 1st of August at 5pm you will most likely hear a siren.