a coin mechanism for vending machines comprising a coin receptacle , a detector for unlocking a dispensing mechanism only when a coin of the proper size is received in the receptacle , and a coin retaining device for retaining coins deposited in the mechanism only when a selected product has been properly dispensed from the machine . the detector includes a wall defining part of a coin slot , a window in the wall , a coin holding lever for holding coins across the window only when such coins are of the proper denomination , and a detector arm for entering the window when it is open to prevent the actuation of the product dispensing mechanism and for enabling the actuation of the dispensing mechanism when the window is closed by a coin .