There are many people who we want in our dorm rooms. We open our doors to prospective students and to roommates’ high school classmates. Sometimes, we lend our futon to a friend who missed the last Quad shuttle of the night. On a very good Friday night, we stumble home with that senior from section.

And then there are people who we don’t want in our rooms—people whose presence makes life decidedly awkward, uncomfortable, or worse. Like room inspectors, who leave us with a handful of pop tarts and no toaster oven. Or arsonists, larcenists, and on unannounced Saturday morning visits, Mom.

Luckily, we have a system that makes it easy to keep out unwanted visitors. First, campus-wide swipe card access ensures that only Harvard affiliates can get into student houses. And second, thanks to the vastly underappreciated invention of the lock and key, only we and our roommates can walk right into our personal suites. Well, we, our roommates, and Dorm Crew.

The beauty of Harvard’s easy two-step system is that as long as everyone sticks to it, it works. Problems arise—such as last week’s attempted burglary in Kirkland—when both lines of defense fail. Swipe-access’s protection is rendered null when we ignore our friendly neighborhood HUPD officer’s admonitions to stop “piggybacking,” and let someone follow us into our house without swiping his or her own ID card. And even doors with locks permit entry when they are propped open by a coat hanger, shoe, or toaster oven.

Yes, asking that guy or gal outside the entryway for ID is awkward. He or she may, in all likelihood, look offended and snap, “I live in your hall!” But consider: Is a little social discomfort worth $10,000 of personal belongings? (This much was stolen from Lowell in 2005.) And, conversely, when your lab partner turns to you outside Old Quincy C and asks for ID, try not to be belligerent. After all, you may look very different without safety goggles.

So when running down to the basement to get laundry, the temptation to use your QR textbook as a doorstop may be overwhelming, but resist! Chances are that your late-night visitor isn’t the cute senior from that party last weekend but instead someone who only loves you for one thing: your iPod. After all, Prince Charming knows to knock.