I believe that footage is most likely stock footage from Cold War era West Germany, particularly in Bavaria, which had a massive system of HLS sirens judging by how the installation looks. Bear in mind that video is from '71 when the British, Americans, and French were still in West Germany keeping an eye on DDR and making sure they weren't up to anything. My dad's brother was in Germany from '79-'80 as a rifleman attached to a border guard division in Western Germany, and he recalls the sirens going off a couple times, usually in co-ordinance with NATO or NVA (East German Army) military exercises.
Here is a list of HLS sirens in Bayern (Bavaria):
http://www.hochleistungssirene.de/index ... iste&bl=11