The present invention relates to a method and an electronic search system for operating an automatic device, preferably an automatic lawnmower. The system comprises at least one first electrical cable (1, 4, 5, 6) connected to at least one first signal generator (3, 7, 8) and at least one sensing system arranged on said device. Said sensing system detects at least one magnetic field being transmitted via said cable (1, 4, 5, 6) and propagating through the air, the sensing system transmitting a processed signal to at least one driving means which contributes to the movements of said device in relation to a surface. Said search system comprises means by which the first signal generator (3, 7, 8) of the present invention transmits a current through said first cable (3, 7, 8), said current during a part of time being is in a state of rest where it is substantially constant, said state periodically being interrupted by at least one first characteristic current pulse.