Abstract: Apparatus (1) for monitoring liquid level in a tank comprises a battery powered monitoring unit (2) for mounting in or on the tank, and a remote display unit (3) which is mains powered. The monitoring unit (2) comprises a microcontroller (8) which operates the monitoring unit (2) alternatively in one of a first operating mode and a second operating mode. During the first operating mode an ultrasonic transducer (7) determines the liquid level at third predefined time intervals of fifteen seconds and operates a radio transceiver (10) to transmit a signal indicative of the liquid level at first predefined time intervals of one hour to the display unit (3). For so long as the microcontroller (8) determines that the liquid level is constant or falling at a normal draw-off rate, the monitoring unit (2) is operated in the first operating mode.