The body scanners rolling out to airports nationwide may violate travelers’ privacy, and they might even cause cancer.

But they prevent terrorists from wreaking havoc. Or do they?

Some research claims the machines — which produce a virtual nude image of the body — might not detect explosives or even guns taped to a person’s body. The U.S. government has reservations about their efficacy, as well. And even proponents of the technology concede the machines are not designed to detect so-called “booty bombs” — explosive devices concealed inside the human body.

Part 1: Are They Constitutional?

Pa...