A device and method rapidly quantifying the relative distention of the bladder of a human subject are disclosed. Ultrasonic transducer 1, which is positioned on subject 2 in proximity to bladder 16, is excited by pulser 3A under command of microprocessor 4 to launch an acoustic wave into patient 2. This wave interacts with bladder walls 12,13 and is reflected back to ultrasonic transducer 1, when it is received, amplified and processed by receiver 3B . The resulting signal is digitized by analog-to-digital converter 5 under command of microprocessor 4, and is stored in data memory 6B. The software in microprocessor 4 determines the relative distention of bladder 16 as a function of the propagated ultrasonic energy; and based on programmed scientific measurements and individual and anatomical and behavioral characteristic of with the specific subject as contained in program memory 6A, sends out a signal to turn on any or all of the audible alarm 7, the visible alarm 8, the tactile alarm 9 , and the remote wireless alarm 10.