Abstract: A system for sensing the level of contents in a container is disclosed. A tubular member is vertically disposed in the container and sealed from the contents of the container. A marker located in the tubular member and generating a peripheral polarized magnetic field, is levitated at the height of float means located around the tubular member buoyed on the contents of the container and generating a polarized magnetic field within the tubular member of like polarity beneath the polarized magnetic field of the marker. A depth transducer located at one end of the tubular member forms part of a pulse-echo ranging system which calculates ranges on the basis of a time lag between emission of an ultrasonic signal by the depth transducer and receipt of at least one return echo signal from the marker in order to determine the depth of the marker in the tubular member, and indirectly, the level of contents in the container.