A robotic work tool system (200), comprising a charging station (210), a boundary wire (250) and a signal generator (240) for generating and transmitting a signal through said boundary wire (250) for demarcating a work area (205), said robotic work tool system (200) further comprising a robotic work tool (100) configured to detect a magnetic field strength (M1, M2) in the work area (205) and said robotic work tool system (200) being configured to adapt a current level of the signal being transmitted through the boundary wire (250) based on the detected magnetic field strength (M1, M2).
