As sturdy deadbolts and reliable window locks have become more common, some crooks have learned that the easiest way to get into a house is to ring the doorbell. So never open the door unless you know who's on the other side. If you don't have windows that let you see who's knocking, install a peephole. Standard peepholes are inexpensive, and are sold at home centers and hardware stores. Installation takes less than 15 minutes, whether your door is wood, steel, fiberglass or a composite material. For a splinter-free hole through a wood door, use a brad point bit. With metal, fiberglass or composite doors, use a standard bit. Run the drill at full speed and press lightly—that creates a clean hole through the outer skin and inner foam core. Most peepholes require a 1/2-in. hole.