Detector /(?)/

De·tect·or

Detector

n.
  1. One who, or that which, detects; a detecter.
    A deathbed's detector of the heart.
  2. An indicator showing the depth of the water in a boiler. (Elec.)

Phrases & Compounds
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.