Audio Door Entry System allows you to speak to callers before you let them in via a door entry phone. The door can then be opened manually or it can be relaeased electronically from a remote location. Video Door Entry systems are equipped with the same features of an Audio entry system, however, these entry system will also display the images of the caller for extra security. Hikvision Intercom Series allows you to see everything that goes on within your home or business and gives you the power to control it at your fingertips. These systems can be used for more than just access control; they also feature unit-to-unit video calling to aid communication between other rooms and buildings.