Light curtain for monitoring a protective field, said light curtain comprising: at least one first optical unit comprising at least one first radiation emitter and at least one first radiation receiver, and at least one second optical unit being opposed to said first optical unit comprising at least one second radiation receiver and at least one second radiation emitter for forming a linear array of radiation beams between the first and second optical unit , said first optical unit comprising a first controller unit and a first communication interface, said second optical unit comprising a second controller and a second communication interface, wherein a first unique identifier is allocated to the first optical unit and second unique identifier is allocated to the second optical unit , and wherein the first and second communication interfaces are operable to exchange communication signals between the first and second optical units , characterized in that each one of the first and second controllers is operable to verify the identifier of the opposing optical unit based on the transmitted communication signals, wherein the first and second controllers are further operable, during a power-up procedure, to determine whether the power-up procedure is a first power-up procedure after installation, if the power-up procedure is a first power-up procedure after installation, to store the first unique identifier in the second optical unit and/or to store the second unique identifier in the first optical unit, if the power-up procedure is not the first power-up procedure after installation, to verify whether the unique identifiers of the first and/or second optical units match with the stored identifiers. at least one first optical unit comprising at least one first radiation emitter and at least one first radiation receiver, and at least one second optical unit being opposed to said first optical unit comprising at least one second radiation receiver and at least one second radiation emitter for forming a linear array of radiation beams between the first and second optical unit , said first optical unit comprising a first controller unit and a first communication interface, said second optical unit comprising a second controller and a second communication interface, wherein a first unique identifier is allocated to the first optical unit and second unique identifier is allocated to the second optical unit , and wherein the first and second communication interfaces are operable to exchange communication signals between the first and second optical units , characterized in that each one of the first and second controllers is operable to verify the identifier of the opposing optical unit based on the transmitted communication signals, wherein the first and second controllers are further operable, during a power-up procedure, to determine whether the power-up procedure is a first power-up procedure after installation, if the power-up procedure is a first power-up procedure after installation, to store the first unique identifier in the second optical unit and/or to store the second unique identifier in the first optical unit, if the power-up procedure is not the first power-up procedure after installation, to verify whether the unique identifiers of the first and/or second optical units match with the stored identifiers. <EOS>