But Ensign Justin Monroe, a teaching assistant at the Naval Academy, used a small wireless receiver to intercept their conversation. With a click, he projected the messages on the screen at the front of the room for the entire class to see.

While their chatter was innocuous — “hello” and “he’s in my company, too” — the implications, Monroe warned the class, were anything but.

“You’re just broadcasting this,” he said. “If you guys were talking about phone numbers, bank information, I would see it.”