Abstract: An acceptor for money items such as coins or banknotes produces a money item parameter signal (x1) depending on a sensed characteristic of the money item. A store (12) provides window data corresponding to normal acceptance ranges of values of the parameter signal for a money item of a particular denomination (NAW), as well as restricted acceptance windows (RAW). A processor (11) determines when an occurrence of the parameter signal (x1) may represent a fraudulent money item and then for subsequent sensed money items compares the value of the parameter signals (x1) with the restricted acceptance range (RAW). The RAW range is used until n succAn acceptor for money items such as coins or banknotes produces a money item parameter signal (x1) depending on a sensed characteristic of the money item. A store (12) provides window data corresponding to normal acceptance ranges of values of the parameter signal for a money item of a particular denomination (NAW), as well as restricted acceptance windows (RAW).