The Collaborative International Dictionary of English v.0.48:

Detector \De*tect"or\, n. [L., a revealer.]
   One who, or that which, detects; a detecter. --Shak.
   [1913 Webster]

         A deathbed's detector of the heart.      --Young.
   [1913 Webster]

   2. Specifically:
      (a) An indicator showing the depth of the water in a
          boiler.
      (b) (Elec.) A galvanometer, usually portable, for
          indicating the direction of a current.
      (c) (Elec.) Any of various devices for detecting the
          presence of electric waves.
          [Webster 1913 Suppl.]

   Bank-note detector, a publication containing a description
      of genuine and counterfeit bank notes, designed to enable
      persons to discriminate between them.

   Detector lock. See under Lock.
      [1913 Webster]