Eye movement are detected with a sensor device attachable to an eyelid. The sensor device may include an arrangement of sensors, including any combination of piezoelectric sensors, accelerometers, and/or any other type of sensor. An external device may be provided for processing sensor data. The sensor device and/or external device may analyze the sensor data to generate eyeball movement data, and to differentiate first directional data and second directional data. The first directional data may be considered as movement occurring substantially horizontally and the second directional data may be considered as movement occurring substantially vertically. The sensor device and/or external device may therefore provide data regarding sleep cycles of the user.
