This is not usually used in homes, but it could be. Most of the time it's used commercially and in apartment buildings. I would venture to say that just about everybody has run into some sort of access control before. Whenever you get buzzed into an apartment building or swipe your card at work to open a door or maybe even type in a code to get through a door. This is access control. Your access to that apartment or into your companies building or office is being controlled via voice communication, a code, or a card reader which sends a signal to a door strike on the door and allows you to open it. Some places even go a few steps further, but it is all access control. If you think about it, your garage door opener is a form of access control. And it too can be controlled by many other things, like a phone in your home, or your mobile phone. Imagine this, a friend or relitive comes to your side door and rings the doorbell, your phones around the house ring, you answer the phone and, from your phone, you open the garage door to let them in! Easy and quick.