Nocturnal incontinence (enuresis) affects 20% of children over four years old, and this figure typically decreases by 15% each year. At the age of 18, 1% of those people remain enuretic. Nocturnal enuresis can be treated by means of a conditioning device that awakens the patient once the urine level has reached a preestablished threshold of the capacity of his or her bladder. We have designed and implemented a portable miniaturized ultrasonic monitor, which permits estimation of the urine volume with an accuracy of 75%. Prototypes have been completed and validated on 41 patients (children) at Ste. Justine Hospital (Montréal). On the first group of 33 patients, we used a hand-held transducer to determine the volume detection range, which is accurate for volumes between 40 and 400 mL. With the second group of 8 patients, the device was mounted on an elastic belt around the abdomen. Measurements were taken in order to validate the accuracy of urine threshold detection and the activation of the corresponding alarm.