A system for detecting the presence of an occupant in a child seat is provided. The system includes at least two sensor modules positioned to detect acceleration of the child seat. The sensor modules provide signals representative of the acceleration detected at the first and send sensor modules to a controller. The controller includes signal processing circuitry for processing the signal to determine whether the signals received from the sensor modules are representative of the physiological motion of the occupant. The controller processes the signals received from the sensor modules to isolate acceleration of the child seat from the motion of the vehicle.