“Ultimately, we’re dealing with people’s intent more than items. Which concerns you more: a person who has no bad intent but who has an item on them like a knife or a gun, or someone who has bad intent but doesn’t have such an item?” he said. “Most people are comfortable with the former rather than the latter. A person with bad intent will find a way to cause damage. A person without bad intent who happens to have an item on them is not the issue.”

Risk-based systems can help solve that problem, but only when used correctly. The most famous and widely used is TSA’s PreCheck, which launched in December 2013. It allows U.S. citizens and permanent residents who submit to a somewhat strict background check (including an in-person meeting and fingerprint scan) to receive expedited screening at airports for five years. Jacobson says the best thing policy-makers could do to airport improve security is get a lot more people into PreCheck.

“The irony is that if we do less overall screening by putting the right people in PreCheck and the people we don’t know anything about not in PreCheck, the total amount of screening done will be less, the amount of technology we use will be less, and the total security of the system will be greater. It’s completely counterintuitive.”