Low power rotational detection methods and apparatus

A wearable user device comprising:

• a first hearing aid configured to be disposed within a first ear of a user comprising a first MEMS accelerometer, a third MEMS accelerometer and a first power source, wherein the first MEMS accelerometer is configured to determine a first plurality of movement data in response to a first head motion of the user, wherein the third MEMS accelerometer is configured to determine a third plurality of movement data in response to the first head motion of the user, and wherein the first power source is configured to provide operating power to the first hearing aid, the first MEMS accelerometer and the third MEMS accelerometer;
• a second hearing aid configured to be disposed within a second ear of the user comprising a second MEMS accelerometer, a fourth MEMS accelerometer and a second power source, wherein the second MEMS accelerometer is configured to determine a second plurality of movement data in response to the first head motion of the user, wherein the fourth MEMS accelerometer is configured to determine a fourth plurality of movement data in response to the first head motion of the user, and wherein the second power source is configured to provide operating power to the second hearing aid, the second MEMS accelerometer and the fourth MEMS accelerometer;
• and
• a processor coupled to the first hearing aid and the second hearing aid, wherein the processor is configured to determine a first plurality of rotation data in response to the first plurality of movement data, the second plurality of movement data, the third plurality of movement data, the fourth plurality of movement data, a first approximate displacement between the first hearing aid and the second hearing aid, a second approximate displacement between the first MEMS accelerometer and the third MEMS accelerometer, and a third approximate displacement between the second MEMS accelerometer aid and the fourth MEMS accelerometer.