On Thursday, 23 October 2014 18:43:04 UTC+3, wrote:
There are accelerometers for all three axis.

Yes, and if you add 3-axis (MEMS) gyros to that, you'll end up with so-called inertial sensors. You can measure acceleration all you want but those sensors alone cannot calculate the direction of acceleration, you need rate gyros for that. And even rate gyros need long-time reference from other sensors, such as 3D-compass + GPS.