Risingon 12V 22MM CAR PARKING SENSOR KIT UNIVERSAL 4 SENSORS BUZZER REVERSE BACKUP RADAR SOUND ALERT INDICATOR PROBE SYSTEM. These systems use either electromagnetic ultrasonic sensors. As an ultrasonic systems relies on the reflection of sound waves, the system may not detect flat objects or object insufficiently large to reflect sound - e.g., a narrow pole or a longitudinal object pointed directly at the vehicle or near an object.