Here discloses a system for sensing bladder volume. The system includes at least one patch, a plurality of light emitters, a plurality of light sensors, and a process. The at least one patch is configured to attach to a human skin or a wearable garment at locations in proximity to an abdomen area. The light emitters are directed towards the abdomen area. The light sensors are configured to receive light signals that are emitted by the light emitters, reflected by human tissues, and transmitted through an abdominal wall. At least one of the light emitters or at least one of the light sensors is disposed on the at least one patch. The processor is configured to receive information of the received light signals and to predict a bladder volume based on the information of the received light signals.
