A nebuliser cup for maintaining a safe level of liquid during nebulization, the cup comprising a liquid level sensor comprising: a first element sensing liquid at or below a position corresponding to a filled liquid level in the nebuliser cup； a second element electrically isolated from the first element and located at a position corresponding to a filled liquid level in the nebuliser cup； and wherein when the cup is not filled with a liquid to the filled liquid level, the first element, the liquid and the second element do not form an electrically coupled circuit； and when the cup is filled with a liquid to the filled to liquid level, the first element, the liquid and the second element together form an electrically coupled circuit.
