The liquid level sensor (1) comprises a disc-shaped piezoelectric body (2) on which is fastened a frustoconically shaped metal part (12) having a plate-shaped end piece (14) at its tapered end. The piezoelectric body (2) is set vibrating mechanically by the application of a radio-frequency electric voltage (V). The vibrations are transmitted via the metal part (12) to the end piece (14) and there lead to bending oscillations. If the end piece (14) comes into contact with a liquid, the oscillations are attenuated. This attenuation or a then increased energy demand can be measured and used for switching measures, e.g. for switching off the liquid delivery. <IMAGE>
