A device for loading and unloading a tool intofrom the tool magazine of a machine-tool or the like comprises a door, which separates the area of the tool magazine from an external protected area, and a tool-bearing slide, which can be displaced between a backed-off position outside the door and an advanced position inside the door and close to the tool magazine. Tunnelling between the first and second quantum dots is controlled by a side gate andor a surface gate. When the weight change is less than a predetermined fraction of either the weight of container weight andor of the liquid originally contained in the container, a signal is generated to indicate that the container may be empty. A voltage control unit controls the voltage increasing unit. As a result, the receiving sensitivity can be improved. The output from the low gain amplifier may be used as a voltage output node that provides a voltage that is an amplification of the voltage produced by the floating signal source.