A car seat occupant detection system for a car seat installed in a vehicle is provided. The system includes at least one harness sensor for detecting whether connectors of a car seat harness are connected and a weight sensor for detecting the weight of an occupant in the car seat. The system includes a controller in communication with the at least one harness sensor and the weight sensor. The system includes a transceiver configured to selectively communicate with a driver device via a local wireless link and with a third party device via a wide area wireless link. The controller determines whether or not an occupant in the car seat has been abandoned by a driver based on detections of the at least one harness sensor, the weight sensor, and communication range status between the transceiver and the driver communication device via the local wireless link.