One night last month in Red Boiling Springs, Tennessee, sheriff’s authorities allege that Lee Clark, 18, and Adam Cisneros, 19, broke into the local high school, managed to breach a locked safe in the office of the school resource officer, and made away with an AR-15 rifle and two bulletproof tactical vests. When I told Dave Goetzinger, a writer and authority on gun storage, in Eugene, Oregon, about the incident, he wasn’t surprised. While authorities aren’t releasing information on the type of safe or how the teens got into it, Goetzinger said that many products sold to store or otherwise secure guns are not as robust as people might think. Indeed, some are so shoddily made that they can be opened with a gum wrapper. Goetzinger never imagined that he would need expertise in storing guns. But four years ago, he decided to get a handgun for personal protection. Ahead of that purchase, he bought a small handgun safe. “The moment I brought it home and took it out of the box, I suspected something was wrong,” said Goetzinger. “All I did was thump on it with a finger, and the thing sounded like an old-style coffee can.” Online, he found a video demonstrating how to break into his new...