The invention relates to measuring devices or display devices and a method for operating these devices, in particular instruments for level measurement, for level detection, for detecting the topology of a product surface or for displaying the measured values of these instruments. A measuring device or display device has an RFID unit. The RFID unit is set up to exchange data with a memory on an external command from an external communication device, to switch a controllable switch on and off, and/or to transfer energy to an energy storage device.