According to certain examples, a circuit-based wireless communications system provides secure access to a vehicle by way of certain circuitry configure to compare a first RF background observed for a vehicle-located RF receiver that is part of a vehicle-located circuit secured to a vehicle, with a second RF background observed for a wireless-communications vehicle-access circuit that includes another RF receiver. In response, a distance metric is generated to indicate a degree of similarity between the first RF background and the second RF background, and based on whether this metric satisfies a threshold, access to the vehicle may be granted via the wireless-communications vehicle-access circuit.