> If it detects 9.8g suddenly going to 0g then it parks the read head as it's probably just been dropped.
9.8g? Is your office inside a centrifuge? :-P
9.8g? Is your office inside a centrifuge? :-P
g already means "9.8 m/s²"
Thus, normal gravity is 1g and free fall is 0g. 9.8g would mean 9.8 times the gravity at Earth surface, that is "96 m/s²". You would feel almost ten times as heavy. For reference:
Jupiter "surface" gravity is 25.9 m/s²
Sun "surface" gravity is 274 m/s²
Lesson: Don't try to take it standing up.
Which is obviously wrong if you think of it as measuring the acceleration of the laptop. The physical acceleration of the laptop is obviously zero when it is at rest on a table. (Acceleration is the change in speed, and the laptop has zero change in speed.)
If you think about the accelerometer as a little micromechanical arm which is being deflected relative to the laptop by the force of gravity, it makes a lot more sense. When they're falling together the deflection is 0.
I gave it some thought, and no, I don't think you can build a self-contained one. But if you allow external communications it becomes very doable (see: GPS system). Also, if you allow another input that tells the device it's orientation wrt. the gravitational field, say a magnetic field sensor, it becomes easy.