boundary markers and a sensor for detecting the boundary markers located on the lawnmower reference is also made to fig1 a 12 b 13 a 13 b 14 a 14 b 15 and 16 which illustrate additional types of boundary markers fig1 a and 11b illustrate the lawnmower 10 with a boundary sensor 80 attached thereto in fig1 a the boundary is marked by a series of markers 82 placed into the ground on the edge of the lawn typically the markers are placed at set distances one from the next alternatively they can be placed close together along portions of the edge which are very curvy and further apart along straighter portions of the edge in fig1 b the boundary is marked by a wire 84 which is marked in some suitable and detectable manner the type of marking matches the type of sensor attached to the lawnmower 10 in one embodiment shown in fig1 a and 12b the boundary markers 82 have a magnet therein in the embodiment of fig1 a the boundary marker 82 is formed of a plastic pin 90 a magnet 92 placed within pin 90 and a plastic cover 94 covering the magnet pin unit in the embodiment of fig1 b the boundary marker 82 is a metallic pin which is magnetized as shown the corresponding sensor 80 for both embodiments is a gauss meter such as the model 4048.