I'm always having trouble figuring out where the front of the car is so I'm contemplating having my dealer install the optional front sensors. My question is how do they work? The rear sensors come on when I put the car in reverse then turn off when I go back to drive. Since the car is usually in drive, what happens when you pull up to a car at a light or a stop sign? How do the sensor know you are just driving and not trying to park?