An apparatus comprising: a first electrode, a central electrode, a second electrode, a first sensing layer placed between the first electrode and the central electrode, the first sensing layer configured to generate a first electrical signal (V 1, R 1) in response to an external stress applied thereto, a second sensing layer placed between the central electrode and the second electrode, the second sensing layer configured to generate a second electrical signal (V 2, R 2) in response to an external stress applied thereto, a circuit (35, 55) connected to the first, second and the central electrodes, said circuit (35, 55) being configured to measure the first electrical signal (V 1, R 1) using the first electrode and the central electrode, and the second electrical signal (V 2, R 2) using the second electrode and the central electrode, the apparatus being characterized in that the first sensing layer comprises piezoelectric crystallites aligned substantially in a first direction parallel to the first sensing layer, and the second sensing layer comprises piezoelectric crystallites aligned substantially in a second direction parallel to the second sensing layer, the first and second directions being non-parallel to one another, and the apparatus being further characterized in that the apparatus is a flexible sensor module attachable to a part of the human body, the apparatus configured to convert an external stress produced by movement of the part of the human body into at least one of the first (V 1, R 1) and second (V 2, R 2) electrical signals for use in controlling an electronic device, a first electrode, a central electrode, a second electrode, a first sensing layer placed between the first electrode and the central electrode, the first sensing layer configured to generate a first electrical signal (V 1, R 1) in response to an external stress applied thereto, a second sensing layer placed between the central electrode and the second electrode, the second sensing layer configured to generate a second electrical signal (V 2, R 2) in response to an external stress applied thereto, a circuit (35, 55) connected to the first, second and the central electrodes, said circuit (35, 55) being configured to measure the first electrical signal (V 1, R 1) using the first electrode and the central electrode, and the second electrical signal (V 2, R 2) using the second electrode and the central electrode, the apparatus being characterized in that the first sensing layer comprises piezoelectric crystallites aligned substantially in a first direction parallel to the first sensing layer, and the second sensing layer comprises piezoelectric crystallites aligned substantially in a second direction parallel to the second sensing layer, the first and second directions being non-parallel to one another, and the apparatus being further characterized in that the apparatus is a flexible sensor module attachable to a part of the human body, the apparatus configured to convert an external stress produced by movement of the part of the human body into at least one of the first (V 1, R 1) and second (V 2, R 2) electrical signals for use in controlling an electronic device,