Abstract: An automated teller machine can use an array of pressure sensors, such as piezo-resistive sensors, to detect the presence of foreign objects, such as staples, paper clips, or rubber bands, in a stack of banknotes. A user can insert a stack of banknotes into an automated teller machine. A pair of opposing clamping surfaces can apply pressure to the stack of banknotes. An array of pressure sensors can sense non-uniformities in pressure over the area of the array. If circuitry coupled to the pressures sensors senses a presence of a high pressure area in the surface area of the banknotes, then the circuitry can generate a signal indicating that one or more foreign objects has been detected. The automated teller machine can then prompt the user to remove the stack of banknotes and remove the foreign object from the stack of banknotes.