Someone ask me how to find out how fast a car is going without tapping anything in the car. I thought for a moment and went blank. I could tell several ways tapping into the car's system but without that ... I'm at a loss.
I thought ... maybe ... by bouncing an ultrasonic pulse to the pavement below? Doppler effect?. This is supposed to be for low speeds ...say 25-65 (miles/hour). Anyone with a not-so-crazy idea want to comment? I just thing I'm way off here.