I’m driving through eastern France, the blip-blip of the lane markers zinging backward through my peripheral vision at about 90 mph. I check the mirrors: nothing there. Pretending to doze off, I let the car drift gently to the left. Just as it begins to veer over the dotted line, the left side of my seat vibrates, activated by an infrared sensor looking at the road paint. Meander right, and it’s my right thigh that gets the warning.