An integrated vehicle communications system for on-board use within a vehicle which may also communicate with external portions of the system which includes miniaturized, self-contained read/write transponders 20, 22, 30 of the type disclosed in Schuermann U.S. Pat. No. 5,053,774, for providing functions within the vehicle, e.g., for sensing conditions and parameters, The on-board interrogation unit 10 interrogates and receives signals by RF communication provided by on-board antennas 14, 26, 28 between the interrogation unit and respective transponders for read/write responder operation. The processor 33 with display device 34a and/or control circuits 34b carries out on-board functions in response to such interrogation. A transponder 22 may serve as a vehicle operator key by which the system may verify key code, unlock the vehicle doors, as well as select and perform initialization functions including ignition, seat and seat belt adjustment, mirror positioning, and antitheft functions before vehicle entry by the operator. A transponder 30 may access external control data for premises or toll access, and may provide toll or credit or service transactions, as for authorization or verification or toll charge debiting purposes. The system may include also IR links.