A transducer for use in a fluid detector for determining a presence of a fluid within a container, the transducer comprising a piezoelectric element that outputs an ultrasonic signal in response to an input electrical signal, characterized in that said transducer further comprises, a lens with an upper portion, a lower portion, and a focal point, the upper portion including a curved surface with convex side. The piezoelectric element is coupled to the upper portion of the lens so that, when the lens is disposed adjacent an outer surface of a wall of the container such that the lens is intermediate the piezoelectric element and the wall, the lens focuses the ultrasonic signal toward the focal point of the lens and on the inner surface of the wall.