It is undetected. Dar bar tells you nothing other than "there's somebody there" -- which 90% of the time means low furballers, NOE dweebs that broke their deck alt, and so on.
It does not tell you "bombers are on their way" -- which in every case in WW2, was known. Heavy bombers did not strike without detection, and whether or not a single part of a bomber stream was attacked entirely depended on how busy the defense fighters were with OTHER parts of the bomber stream.