Reinforced cockpit doors with strict policies in place for when the pilots can open it, which is what we do now (in the U.S. at least) even with all of the TSA stuff.
This source[1] claims that the probability of getting hijacked while on a commercial flight is 0.000004%. On the other hand, the case fatality rate of covid-19 is around 2% based on what I'm able to find.
So why are we worried about possible plane hijackings when a lot of people don't seem to be overly worried about something that's many times more risky.
