Novel techniques for averting unsanctioned access to on-board vehicle networks include obtaining indications of detected stimuli and/or conditions that are external to a target computing device, and determining whether or not the detected stimuli/conditions are indicative of the target computing device being utilized, operated, held, and/or carried by a person on-board the vehicle. External stimuli/conditions may include signals transmitted by other devices on-board the vehicle, ad-hoc data received via various interfaces of the target computing device, comparisons of vehicle heuristic data with data generated by components of the target computing device, etc. A confidence score may be generated (e.g., over time) based on detected stimuli/conditions. Access of the target computing device to an on-board vehicle network may be granted or denied based on the detected stimuli/conditions and/or the confidence score. Further, the novel techniques are not required to use any user input.