A system is disclosed for detection of whether a movable object, such as a sports object, e.g. a football or an ice hockey puck, has passed a flat plane in space, such as a goal plane defined e.g. as a vertical plane extending from a goal line or a horizontal plane defined by the upper rim of the basketball basket The system comprises a plurality of pairs of antennas arranged along the periphery of the flat target plane, the two antennas of each of said pairs being arranged with a mutual displacement in the direction perpendicularly to the flat target plane, radio wave emitter means arranged in the movable object and/or each antenna, and means for receiving the radio waves from the radio wave emitter means and provide an output accordingly arranged in each antenna and/or in the movable object, the system further comprising processing means to receive and process said output together with a predetermined set of conditions and providing a resulting output if the set of conditions are fulfilled so as to determine whether the movable object passes the flat target plane.