The Swann SW244-BVD video intercom system lets you see and hear who's calling at your door before you open it. When the door bell is pressed, the image of the caller instantly appears on the high resolution monitor. You can then push the talk button to hear and speak with that person. You can also hit the door strike button to unlock the door, provided your door is equipped with a door strike mechanism. The camera part of this system is equipped with IR illumination and will provide you a clear image of your caller even in the dark. The camera is also weatherproof and incorporates an anti-theft design to discourage tampering. There's also an alarm button on the main unit that you can activate to deter an unwanted visitor.