Abstract: The invention may be said to consist in a level sensor 1 for providing an indication of liquid level in a container comprising: an ultrasonic transducer 120 for emitting an ultrasonic signal to the surface of the liquid and for detecting a return signal, reflected from the surface, a controller 19 that instructs the transducer 120 to emit ultrasonic signals and receives an indication that a return signal has been detected, the controller 19 comprising a timer for measuring the time period between emission of the ultrasonic signal and receipt of a return signal, the determined time period providing an indication of the liquid level, and a radio transmitter 22 that receives an indication of the liquid level and transmits a radio liquid level signal comprising the level indication to a remote output unit e.g. 200.