Abstract: A detector mechanism and system for currency dispensers for automatic banking equipment which senses the presence of multiple or double bills, called "doubles," at any bill location in a series of bills intended to be fed one by one in a path of travel from a supply of bills to a place of delivery to a customer. The bill thickness of each bill is gauged continuously while moving in the path of travel, and the thickness measurements are time averaged over substantially the entire length of the gauged portion of the bill. The averaged and normal bill thicknesses are compared to determine if the averaged thickness is greater than the normal thickness by a predetermined amount. A greater thickness determination generates a signal of the presence of doubles, and the signal actuates means to reject the doubles while moving in the path of travel before delivery of the doubles to a customer.