A self-powered urinary-incontinence sensor with a flexible wire-type urine-activated battery has been developed as an application for wireless biosensor networks. It is disposable and can be embedded in a diaper. The battery consists of two long film-type line electrodes printed on a flexible plastic sheet that abuts the absorbent material of the diaper. It conforms to the shape of the diaper when the diaper is worn. The stress produced by the curvature of the diaper presses the electrodes firmly against the diaper material, providing greater contact with any urine present. Thus, the battery generates more power than when it is flat, as in an unworn diaper. To verify the effectiveness of the battery, we fabricated a battery and a prototype sensor, which consists of an intermittent-power-supply circuit and a wireless transmitter, and embedded the battery in a diaper. The anode of the battery also acts as a wide ground plane for the antenna of the wireless transmitter, which radiates a large amount of power. When 80cc of urine is poured onto the diaper, the battery outputs a voltage of around 1V, which allows the sensor to transmit an ID signal over a distance of 5m every 40 seconds or so.