The market is expected to grow through 2020, and there's no sign it will slow down after that. In the science fiction movie "Gattaca," Ethan Hawke's character was able to get into a secure area using nothing but a scan of his retina. That technology actually exists today. It's called biometrics. In addition to your eyes, it can scan your fingerprints or recognize your voice. It's a great choice for people with fat bank accounts who harbor government secrets, but for the rest of us, digital door locks offer a cheaper home security option. Digital door locks can be opened with an electronic "smart key" or a remote, or you can open them by typing numbers on a pin pad. These locks are almost impossible to pick. Burglars want to get in and out of a house as quickly as possible. The longer it takes to enter a home, the more likely someone will notice and call the police. So the harder you make it to gain entry, the better.