A device for checking the concentration of clear rinsing agent in a rinsing liquid circulated in the means for retaining water of a household appliance is provided. The device includes a processing unit operatively connectable to a sensor having at least one transmitting element that emits an optical signal and at least one receiving element that receives the optical signal emitted by the transmitting element. The processing unit determines the wetting of the sensor with clear rinsing liquid and renders an estimate of the concentration of clear rinsing agent in the clear rinsing liquid as a function of the wetting of the sensor with clear rinsing liquid based upon the energy level emitted by the transmitting element and received by the receiving element.