It has visual motion detection, through the image sensor, plus a g-sensor (accelerometer).
I don't think Viofo publish the g-sensor data, probably because their g-sensor is never in the correct orientation, it is at whatever angle the windshield is at, and they don't know how to translate that into standard X,Y,Z forces.
I've never seen a dashcam that gives very useful g-sensor data anyway, it tends to be heavily filtered and nothing like reality. If you want to calculate acceleration, you are probably better off looking at the GPS data, and adjusting for it normally being between one and two seconds behind reality. The GPS is pretty accurate most of the time, so can calculate acceleration, whereas no dashcam has a g-sensor that you could work out your speed from.
