The gyro won't do much for you, as it measures rate of rotation, and drifts with an offset. The acceleration sensor is more useful, but it detects the acceleration due to gravity, added to acceleration due to other forces as a 3D vector.
The usual method of detecting a change in motion is to calculate the total acceleration, which is, for floating point acceleration values:
float acc_tot = sqrt (ax*ax + ay*ay + az*az);
and compare that to the resting value.