Many of these alarm sounds came from Jimmy Shields, the original sound designer that worked on Ridley Scott's "Alien" (1979). Jimmy passed away in 2000, but his samples were brilliantly mixed by Byron Bullock and Sam Cooper of CA, with the resources at Pinewood Studios.
(OT: I also have new videos coming - including my finished "Mission 2" mod with alien, motion tracker, and every weapon item + ion torch).