Techniques are provided for validating a mobile device in a passive digital key system. An example method of validating a mobile device includes determining a positioning measurement for the mobile device relative to a reference point, obtaining a measured distance with at least a first transceiver, obtaining a calibration distance based at least in part on the positioning measurement for the mobile device, computing a validation distance based at least in part on a difference between the measured distance and the calibration distance, and validating the mobile device based at least in part on a comparison of the validation distance and a threshold value.