a noninvasive ultrasonic liquid level indicator for indicating the level of a liquid in a reservoir is disclosed which comprises an ultrasonic transducer assembly , structures for holding the transducer assembly in a dry coupled attachment with the reservoir at selectable locations against an exterior surface of the reservoir , and a monitor for revealing a change in liquid height . the transducer assembly conveys signals regarding changes in liquid height to a monitor which warns the user in time to add more liquid or replace the reservoir before the liquid supply &# 34 ; runs dry .&# 34 ; the manners for holding the assembly in place include , but are not limited to , a strap , a clamp , or adhesive material , such as tape . these allow the user to selectively place the transducer assembly along the reservoir at the desired triggering point .