A computer-implemented method includes receiving a request from a mobile device to activate a recognition sequence. The method also includes transmitting a plurality of time-stamped recognition codes to the device, responsive to the request. The method further includes receiving an acknowledgement following transmission of a proper recognition code. The method also includes calculating a time-delay between transmission of the proper recognition code and acknowledgement receipt. The method additionally includes receiving a key-code from the device and comparing the key-code to a code exchanged with the device when the device was previously present within a vehicle. Further, the method includes measuring the received strength of multiple wireless signals successively received from the device and conditional on the time-delay being below a predefined threshold, verification of the key-code and the received signal strength of multiple wireless signals matching a predefined pattern of increasing signal strength, providing vehicle system access to the device.