If you’ve seen some of the ads in the BART stations… or San Francisco Mayor Daniel Lurie’s posts on Instagram… you may notice an emphasis on safety and security in the city. But if you go back in time, there's physical evidence that this rhetoric isn’t new. You can find it in neighborhoods all over the Bay.

Take the Sunset district, on San Francisco's westside, where almost every house has a heavy iron gate. KALW’s Rae Kim went right up to the proverbial front door to find out how those gates got there—and what they might be keeping out.