Whatever system that you put in place would have to never (or very close to never) have a false negative during normal aircraft operation. One other commenter

Whatever system that you put in place would have to never (or very close to never) have a false negative during normal aircraft operation. One other commenter here mentions a simple ignition key would have prevented this incident, but there's been at least one major ignition system flaw in cars that caused multiple deaths ( https://en.wikipedia.org/wiki/General_Motors_ignition_switch_recalls https://en.wikipedia.org/wiki/General_Motors_ignition_switch... ), and the consequences of a failure causing loss of control to a passenger aircraft far outweighs that in a car. Given the very low rate of unauthorised takeoffs of passenger aircraft, and that this case was an insider who may have been able to gain access to keys/codes anyway, is introducing introducing a new system to aircraft justified?