Sensor arrangement, which comprises measuring electronics and a sensor structure that can be fitted onto a base, the sensor structure comprises at least one sensor, and the arrangement is adapted to determine, by means of the data measured by the measuring electronics and the sensor, whether the moisture of the base has changed, and the arrangement is further adapted to determine, on the basis of the data measured by the measuring electronics and the sensor, the presence of a person on the base, characterized in that the sensor comprises electrodes which electrodes to be used in measuring the change in moisture are in the same sensor structure as the structure detecting the force exerted on the sensor by a person, the sensor of the sensor arrangement comprises at least three electrodes (401, 402, 403), which are insulated from each other and arranged in such a way that the arrangement is adapted to determine the moisture level by measuring the resistance between the first and the second electrodes, and to determine a presence by means of the force exerted on a sensor by measuring the capacitance between the first and the third electrodes and/or between the second and the third electrodes, the sensor arrangement is adapted to determine a change in the moisture of the base by measuring the resistance between the electrodes and by comparing it to a reference value that has been measured and recorded when the base was dry, and the sensor arrangement is adapted to determine a presence by measuring the capacitance between the electrodes and by comparing it to a reference value that has been measured and recorded when the base was empty. the sensor structure comprises at least one sensor, and the arrangement is adapted to determine, by means of the data measured by the measuring electronics and the sensor, whether the moisture of the base has changed, and the arrangement is further adapted to determine, on the basis of the data measured by the measuring electronics and the sensor, the presence of a person on the base, characterized in that the sensor comprises electrodes which electrodes to be used in measuring the change in moisture are in the same sensor structure as the structure detecting the force exerted on the sensor by a person, the sensor of the sensor arrangement comprises at least three electrodes (401, 402, 403), which are insulated from each other and arranged in such a way that the arrangement is adapted to determine the moisture level by measuring the resistance between the first and the second electrodes, and to determine a presence by means of the force exerted on a sensor by measuring the capacitance between the first and the third electrodes and/or between the second and the third electrodes, the sensor arrangement is adapted to determine a change in the moisture of the base by measuring the resistance between the electrodes and by comparing it to a reference value that has been measured and recorded when the base was dry, and the sensor arrangement is adapted to determine a presence by measuring the capacitance between the electrodes and by comparing it to a reference value that has been measured and recorded when the base was empty.