you may need two ,..one for send and one for receive to get better resolution .
there are kits on ebay for cars that contain 4 units
http://www.ebay.com/itm/4-Parking-Sensor...YT&vxp=mtr
there are kits on ebay for cars that contain 4 units
http://www.ebay.com/itm/4-Parking-Sensor...YT&vxp=mtr