Detecting device for detecting a state of a diaper, comprising: a sensor unit comprising a conducting unit including at least two electrodes, the electrodes being configured to detect electrical parameters (R, L, C, Z) of their environment, and a carrier layer to which the conducting unit is attached; and a measuring device comprising an input portion being connectable to the sensor unit, a processor configured to receive signals corresponding to values of the electrical parameters (R, L, C, Z) detected by the sensor unit and to process said signals, a power control means configured to control electrical power supplied from a power supply, and a determination means configured to determine, based on evaluating the processed signals using predetermined thresholds of the electrical parameters during predetermined time periods, whether a state of a diaper has changed; characterized in that the sensor unit further comprises a coupling portion on at least one end side of the conducting unit, the coupling portion being connectable to the measuring device; the measuring device further comprises a transmitting means arranged for transmitting information regarding the determined state change to a receiving means; the processor of the measuring device is configured to perform a resonance scan, during which a periodic signal is sent to the sensor unit at a plurality of frequencies; the power control means is configured to apply a sinusoidal alternating voltage to the electrodes; the power control means is configured to set the periodic signal for resonance scan to preset frequencies, which are set so as to correspond to respective resonance frequencies of predetermined substances or ingredients of the substance, thereby causing resonance oscillation of the substance or ingredient of the substance; and the processor is configured to evaluate the received electrical parameters, wherein it is determined that a predetermined substance is present in the space between the electrodes of the conducting unit, when the evaluated electrical parameter is within a range that is preset with regard to said predetermined substance. a sensor unit comprising a conducting unit including at least two electrodes, the electrodes being configured to detect electrical parameters (R, L, C, Z) of their environment, and a carrier layer to which the conducting unit is attached; and a measuring device comprising an input portion being connectable to the sensor unit, a processor configured to receive signals corresponding to values of the electrical parameters (R, L, C, Z) detected by the sensor unit and to process said signals, a power control means configured to control electrical power supplied from a power supply, and a determination means configured to determine, based on evaluating the processed signals using predetermined thresholds of the electrical parameters during predetermined time periods, whether a state of a diaper has changed; characterized in that the sensor unit further comprises a coupling portion on at least one end side of the conducting unit, the coupling portion being connectable to the measuring device; the measuring device further comprises a transmitting means arranged for transmitting information regarding the determined state change to a receiving means; the processor of the measuring device is configured to perform a resonance scan, during which a periodic signal is sent to the sensor unit at a plurality of frequencies; the power control means is configured to apply a sinusoidal alternating voltage to the electrodes; the power control means is configured to set the periodic signal for resonance scan to preset frequencies, which are set so as to correspond to respective resonance frequencies of predetermined substances or ingredients of the substance, thereby causing resonance oscillation of the substance or ingredient of the substance; and the processor is configured to evaluate the received electrical parameters, wherein it is determined that a predetermined substance is present in the space between the electrodes of the conducting unit, when the evaluated electrical parameter is within a range that is preset with regard to said predetermined substance.