Urinary incontinence is a troubling disease that makes it difficult for patients to live a normal life. Rapid detection of urinary incontinence could allow many patients with this condition to feel more confident about going out. Therefore, our goal is to develop a urinary incontinence detector based on a light-emitting diode and a photodiode. Here, we describe the development and testing of a prototype model. The photosensor is driven by a 9 V battery and consists of an ordinary electrical circuit, a light-emitting diode (lambda max = 950 nm), a photodiode (spectrum 750-1200 nm), a comparator and, a compact motor. Light transmission through the underwear was changed by soaking with liquids. This phenomenon was measured using a digital voltmeter. The urinary incontinence sensor was placed on a dummy. Liquids were drained into the shorts. These increased in voltage from 3.73 V to 8.78 V, which caused the motor to vibrate. These results show that the prototype sensor can be used to detect urinary incontinence.