A sensor device determines an amount of liquid contained or stored in an object to be tested. The sensor device contains at least one heating element and at least one humidity sensor. When operated, the sensor device defines at least one volume which can be sealed off by placing the device on the surface of the object to be tested. The heating element is configured to heat at least part of a surface of the object delimiting the volume, the humidity sensor measuring the humidity in the interior of the volume.
