Principle for LDW
(The figure is schematic - not model specific.)
LDW consists of a camera that detects the side lines painted on the road/lane.
If the vehicle crosses the left or right-hand side line of the carriageway without due cause then the driver is alerted by an acoustic signal.
The driver is only warned once each time the wheels cross a line. So there is no acoustic alarm when there is a line between the car's wheels.