On the day the international student moved in, he asked at the front door. "Where is the key?" There was no key. The door opened when you pressed a code on the small device next to it. ## What if the batteries run out, how do you open the door? Keypad door locks run on batteries. When the batteries run out, pressing the buttons does nothing. For those times, many door locks have an emergency terminal on the bottom of the outside panel. If you touch a 9V battery to it, power flows in briefly, and if you press your code then, the door opens. It differs from product to product, so be sure to check the manual. When the batteries get weak, there's usually a warning beep. If you hear that sound, replace them right away. ## Why Numbers Instead of Keys? Korea has a lot of apartments, so all the doors look similar. And if you lose your key or leave it behind, you have to call a locksmith. A code is convenient because you don't have anything to carry around. Families use the same code, so there's also less need to share keys. ## Change the Code on Your First Day After Moving Convenient as it is, there are also things to be careful about. You can memorize the number just by looking at it. The person who lived there before or a worker who came for construction might already know it. That's why Koreans set a new password first thing on moving day. The method is in the manual or the manufacturer's instructions. Avoid easy numbers like your birthday or 1234. It's just one small number, but protecting our home has changed from "remembering to bring the key" to "remembering the code."