Warning wheel

from The Collaborative International Dictionary of English v.0.48

Warning \Warn"ing\, a.
   Giving previous notice; cautioning; admonishing; as, a
   warning voice.
   [1913 Webster]

         That warning timepiece never ceased.     --Longfellow.
   [1913 Webster]

   {Warning piece}, {Warning wheel} (Horol.), a piece or wheel
      which produces a sound shortly before the clock strikes.
      [1913 Webster]