That is called special pleading logical fallacy. There is no imagining anything about an accelerometer. It reads acceleration or do you deny that? To have constant velocity, you need constant acceleration. It is constant because each second (time), the same measure is applied to keep the same speed. Changes in acceleration (called jerk rate) would be different amounts of force applied over time instead of same amount. When you start your car, your acceleration is higher until you get to the cruising speed and then to maintain the cruising speed requires the same acceleration/force applied.