The invention concerns a device for detecting crossing of a line delimiting a zone on a surface, comprising at least two transmitters (7.1, 7.2) of electromagnetic beams (11.1, 11.2) and two sensors (10.1, 10.2) positioned in correspondence with the transmitters to receive a reflected part of the transmitted beams, the transmitters being positioned relative to each other in order that the beams intersect each other.
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