A moveable barrier system includes a loop detector for providing an electrical field. The electrical field has an associated base frequency. The base frequency changes when a vehicle enters the loop detector and the loop detector detects this change. A transmitter device is positioned at the vehicle. The transmitter detects the base frequency of the electrical field as the vehicle becomes positioned in proximity to the loop detector. The transmitter responsively transmits a coded signal to a moveable barrier operator when the base frequency is detected. The coded signal is operable to actuate the moveable barrier operator.