1. A method of determining the state of a restraint system provided within a vehicle, the method comprising: incorporating one or more marker components into a restraint system component located within the vehicle; receiving sensor data associated with the position of one or more of the marker components; and determining, with a processor, a state of the restraint system, along with a physical characteristic of an occupant using the restraint system, based on the position of the one or more marker components from the sensor data; wherein the sensor data is received from a sensor located within the vehicle in a position in which it can observe a plurality of the restraint system components.