Backup Sensors
Backup sensors will alert you  if there is an obsticle in your path
while backing up. Whether a bicycle, another vehicle, or a child, a
backup sensor system will detect the obstacle and give you an
audible tone to alert you. The closer you come to the obstacle, the
quicker the beeping becomes. Sensors are stylishly flush mounted in
the rear bumper, and become active when the vehicle is in reverse.
Systems are very affordable, and are available with either two, or
four rear sensors.