A device (10, 40, 70, 100, 140) for monitoring a monitored zone (12, 154) having - at least one reference structure (30, 90, 130, 152) for generating reference light (32, 52, 82, 132, 160) having a specified spectral characteristic; - a spectrally sensitive optoelectronic sensor comprising at least one light receiver (20, 62, 92, 120, 144a,..., 144n) for detecting received light (38, 58, 88, 138, 158) from the monitored zone (12, 154) and for generating received signals from the received light (38, 58, 88, 138, 158), wherein the received light (38, 58, 88, 138, 158) comprises the reference light (32, 52, 82, 132, 150) and/or object light (36, 56, 86 136, 164) remitted and/or reflected by objects (34, 162) in the monitored zone (12, 154) and a control and evaluation unit (24, 124, 150) for controlling the light receiver (20, 62, 92, 120, 144a,..., 144n) and for receiving the received signals, wherein the control and evaluation unit (24, 124, 150) is configured to determine a detected spectral characteristic of the received light (38, 58, 88, 138, 158) from the received signals, to compare the detected spectral characteristic of the received light (38, 58, 88, 138, 158) with the specified spectral characteristic of the reference light (32, 52, 82, 132, 160), and to trigger a safety directed action on a predetermined deviation of the detected spectral characteristic, characterized in that the spectrally sensitive optoelectronic sensor is designed as an imaging spectral sensor for the spatially resolved determination of spectral data of the objects (34, 162) in the monitored zone (12, 154) and in particular of the reference structure (30, 90, 130, 152). - at least one reference structure (30, 90, 130, 152) for generating reference light (32, 52, 82, 132, 160) having a specified spectral characteristic; - a spectrally sensitive optoelectronic sensor comprising at least one light receiver (20, 62, 92, 120, 144a,..., 144n) for detecting received light (38, 58, 88, 138, 158) from the monitored zone (12, 154) and for generating received signals from the received light (38, 58, 88, 138, 158), wherein the received light (38, 58, 88, 138, 158) comprises the reference light (32, 52, 82, 132, 150) and/or object light (36, 56, 86 136, 164) remitted and/or reflected by objects (34, 162) in the monitored zone (12, 154) and a control and evaluation unit (24, 124, 150) for controlling the light receiver (20, 62, 92, 120, 144a,..., 144n) and for receiving the received signals, wherein the control and evaluation unit (24, 124, 150) is configured to determine a detected spectral characteristic of the received light (38, 58, 88, 138, 158) from the received signals, to compare the detected spectral characteristic of the received light (38, 58, 88, 138, 158) with the specified spectral characteristic of the reference light (32, 52, 82, 132, 160), and to trigger a safety directed action on a predetermined deviation of the detected spectral characteristic, characterized in that the spectrally sensitive optoelectronic sensor is designed as an imaging spectral sensor for the spatially resolved determination of spectral data of the objects (34, 162) in the monitored zone (12, 154) and in particular of the reference structure (30, 90, 130, 152).