Dual-Way communication between monitor and camera, monitor and monitor; support call transfer among all the monitors. You can answer the door and unlock via all indoor monitors, it is convenient and widely used in apartments, villas, hotels and offices. Support connect with additional 2x CCTV camera, 2x PIR alarms, 2x electronic locks, giving you more comprehensive protection for your home.The extension wire is not included in the box, but we will provide the 4 pin connector for you connect the extension wires. You can use RVV4(4 core wire)/Cat5/Cat6 wires to extend the distance for monitor to doorbell, monitor to monitor according to your need, maximum distance 100-200 meters. This item is in the category "Home & Garden\Home Improvement\Building & Hardware\Doors & Door Hardware\Smart Doorbells & Locks\Smart Doorbells". The seller is "arrabin-0" and is located in this country: US. This item can be shipped to United States.