> how fast you drive, even if you don't have a smart car, because your phone contains an accelerometer

Minor nitpick: you can't measure speed with an accelerometer, at least not with a cheap one like the one in your phone. I mean, in theory you can numerically integrate the acceleration to get the speed, but in practice the noise will be so big as to render the result useless after a few seconds. It's much better to have a GPS and derive the speed from the position.

Signed: someone who spent too long programming an IMU and fighting with stupid bosses full of misconceptions.

Other than that, I totally agree with your comment.