Abstract: A coin handling apparatus contains a standard reference coin and a coin validation circuit that compares an inserted coin or slug with the reference coin as it passes through a chute toward a coin gate. The coin gate deflects the coin into a first path if the inserted coin is undersized and otherwise into a second path. The validation circuit produces a "valid coin" signal that indicates a match between the inserted coin and the reference coin, a "coin present" signal if any coin is being compared with the reference coin, and a photodetector output signal, all of which are applied as inputs to a surveillance circuit that analyzes those three signals and generates an output indicative of whether the inserted coin is being "strung", an output indicative of whether the inserted coin is a slug, and an "alert" signal that indicates whether either the coin is being strung or the inserted coin is a slug.