The apparatus is a vehicle motion detection apparatus for short driveways
which uses passive ferromagnetic detecting coils reacting to the
fluctuation in the earth's magnetic field caused by moving vehicles. The
preferred embodiment of the invention uses two sensor coils located on a
line that is approximately perpendicular to the adjacent road and
parallel to the driveway. The sensor coils are designed and connected so
that they generate signals of opposite polarity so that together they
cancel out the signals generated by vehicles on the road, but the signals
generated by a vehicle moving on the driveway do not cancel each other
and are electronically processed.