Simply place the ultrasonic transmitter on the interior of the and trace the exterior of the vehicle with the ultra sensitive receiving device that is attached to headphones so that an possible leak can be detected. A sharp increase in noise notifies that their could be a possible leak in the urethane. The ultrasonic wavelengths will not transfer through the body of the vehicle or the glass but will transfer the small voids and thin pockets of urethane. It is recommended to remove any detachable moldings or cowling materials prior to detection. Perfect for post inspection work!