The CAS-4F is the most advanced  sonar system on the market today.

The CAS-4F Vehicle Reversing Aid is an automatic back up alert system that warns drivers of potential obstacles while backing up their vehicle. Using ultrasonic echo location sonar technology the system is activated when the driver engages reverse gear. A 4 zone variable audio pulse alerts the driver of potential obstacles. The audio pulse intensity increases and the audio frequency changes as the vehicle backs closer to the obstacle. Additionally and exclusively, the CAS-4F includes a VDI (Voice Distance Indicator) module and uses an audible voice to inform the driver how close the rear of the vehicle is from the obstacle calling out the distance in feet starting at 12 ft then 9 ft,6 ft, 5 ft., 4 ft, 3 ft, 2 ft, 18 inches, 12 inches, and if you get less than 12 inches it sounds "CRASH".As with all sensing systems there are blind areas in the sensing patterns due to the cone or triangular nature in the way the sonar pulse is emitted. Whenever an object moves from a covered area and into one of these blind areas a special warning alert message and a very loud tone “OBJECT IN BLIND AREA” will be transmitted twice or until the operator takes the vehicle out of reverse. This is especially helpful for detecting moving objects such as a pedestrian, an animal, a forklift or other moving vehicles that may be behind your vehicle and in harm’s way.