Apparatus and method for monitoring the status of a multiple part vehicle are disclosed. Apparatus according to the invention comprises a tag on a second part of the vehicle which impresses a unique ID code of the vehicle's existing electrical system. An interface unit in a first part of the vehicle detects the presence of a valid ID code on the vehicle's electrical system and in response provides an indication that the second part of the vehicle is connected. A mobile satellite transmitter provides data indicative of the status of the vehicle to an earth station via a satellite. Vehicle position data is also provided to the earth station with each transmission.