Apparatus comprising: a flexible touch panel comprising a layer of piezoelectric material arranged between a plurality of first electrodes (7, 8) and at least one second electrode (8, 14); a device connected to the first electrodes and configured: to receive piezoelectric signals from the first electrodes; to determine whether the received piezoelectric signals are indicative of a change in a bending state corresponding to one or more radii of curvature ( R 1, R 2) of the flexible touch panel; in response to the received piezoelectric signals are indicative of a change in the bending state: to determine a change in the one or more radii of curvature based on tracking a total duration and/or a total charge associated with the bending state (S7,..., S10); and to output the change in the one or more radii of curvature; in response to the received piezoelectric signals are not indicative of a change in the bending state and the flexible touch panel apparatus is in an awake mode: to determine locations corresponding to one or more user interactions based on the received piezoelectric signals and/or capacitance measurements of the first electrodes; and to output the locations corresponding to one or more user interactions. a flexible touch panel comprising a layer of piezoelectric material arranged between a plurality of first electrodes (7, 8) and at least one second electrode (8, 14); a device connected to the first electrodes and configured: to receive piezoelectric signals from the first electrodes; to determine whether the received piezoelectric signals are indicative of a change in a bending state corresponding to one or more radii of curvature ( R 1, R 2) of the flexible touch panel; in response to the received piezoelectric signals are indicative of a change in the bending state: to determine a change in the one or more radii of curvature based on tracking a total duration and/or a total charge associated with the bending state (S7,..., S10); and to output the change in the one or more radii of curvature; in response to the received piezoelectric signals are not indicative of a change in the bending state and the flexible touch panel apparatus is in an awake mode: to determine locations corresponding to one or more user interactions based on the received piezoelectric signals and/or capacitance measurements of the first electrodes; and to output the locations corresponding to one or more user interactions. to receive piezoelectric signals from the first electrodes; to determine whether the received piezoelectric signals are indicative of a change in a bending state corresponding to one or more radii of curvature ( R 1, R 2) of the flexible touch panel; in response to the received piezoelectric signals are indicative of a change in the bending state: to determine a change in the one or more radii of curvature based on tracking a total duration and/or a total charge associated with the bending state (S7,..., S10); and to output the change in the one or more radii of curvature; to determine a change in the one or more radii of curvature based on tracking a total duration and/or a total charge associated with the bending state (S7,..., S10); and to output the change in the one or more radii of curvature; in response to the received piezoelectric signals are not indicative of a change in the bending state and the flexible touch panel apparatus is in an awake mode: to determine locations corresponding to one or more user interactions based on the received piezoelectric signals and/or capacitance measurements of the first electrodes; and to output the locations corresponding to one or more user interactions. to determine locations corresponding to one or more user interactions based on the received piezoelectric signals and/or capacitance measurements of the first electrodes; and to output the locations corresponding to one or more user interactions.