When it comes to building safety, few components are as critical—or as misunderstood—as the hardware on your exit doors. You’ve likely seen the horizontal bars on doors in shopping malls, hospitals, and theaters. You might know them as "panic bars," "crash bars," or "push bars." But does every fire exit door require one?

Have you ever walked past a commercial building and wondered how those large, horizontal metal bars on the doors actually work? More importantly, if their primary job is to let people out quickly during an emergency, how do you keep unwanted visitors in?