Feature: 1. The GSM‑KEY‑4G system is a security system based on the cellular network. The GSM‑KEY‑4G system is used in conjunction with the caller ID. When the authorized number calls, the system will identify the caller and open the door. 2. GSM-Key-4G is integrated with a professional, industrial-grade 4G engine and can receive calls with its SIM card number just like any normal 4G phone. Built‑in 4G module, can work anywhere in the world through 4G, 3G and GSM Net. 3. GSM‑KEY‑4G has a memory. The maximum number of people who can open the door is 200. When GSM‑KEY‑4G receives a call, it will check the calling number and whether the number is in the list. Support power failure alarm for rechargeable battery (battery not included). 4. GSM-key-4G doesn't have the same limitations as regular remote controls. Using your mobile phone, you can even open it from far away, or even from another city! When the door is already open, it is very convenient to reach the door without waiting. 5. With two independent relay switches, and by dialing its mobile phone number to activate the No.1 relay switch, it will reject the call without answering and open the device connected to it, so there is no call charge when dialing this phone, it will recognize the authorized phone number being called, and refuse to answer the call without answering. Specification: Item Type: Remote Control Box Material: ABS Working Voltage: AC 110V - 220V. Package List: 1 x Remote Control Box 1 x Antenna1 x USB Data Cable1 x USB Programming1 x Manual