Metal detectors don't detect crazy people. They detect metal objects and alert when the mass meets or surpasses a certain threshold. So, what Hannity proposes is identifying GUNS. That is the sole indicator of a threat, because you don't know anything else about the person being screened.
THEN he says the rush to blame GUNS is sad and pathetic. He's just a freewheeling bullshitter who counts on an audience incapable of independent thought. He'll say anything to confirm their bias because there's lots of money in it. Hannity is not stupid, he simply has no use for the truth.