Abstract: An automatic bathtub overflow shutoff system detects sustained water flow through a bathtub overflow drainpipe and automatically stops water supply to the bathtub in response. The system includes a tee pipe connector installed in-line along the overflow drainpipe below the overflow drain opening, a flow switch sensor positioned within a sensor port of the tee pipe connector to detect active water flow, a flow switch, a controller, and a first electronic shut off valve on a hot water supply line and a second electronic shut off valve on a cold water supply line. When overflow water flows through the tee pipe connector and is detected by the flow switch sensor, the flow switch signals the controller, which transmits a valve-close command to simultaneously close both supply valves, thereby terminating water entry into the bathtub.