The Hikvision HID-KIS703Y-P 2 wire intercom bundle features a single button door station and a 7" screen room station. This is great for upgrades as the connection between these stations is a basic 2 wire cable run and the room station's WiFi connectivity also allow it to call the Hik-Connect app. Power to the sysem only requires the provided PSU to be connected to the room station, which also powers the door station. The system cannot be expended to add extra door or room stations, keeping it simple.