1850/900/1800/1900MHz four-band, can work in the global GSM network. 2No telephone charges. When the GSM relay switch receives the call from the authorized number, the first 3Security. Use caller ID for identification, unknown callers will be ignored. 4Add or delete users through SMS text commands. 5Relay action confirms the return message to the host or authorized call in the number. This function can be edited by the user.This GSM door opener has the function of remote switch. It can be operated from anywhere by authorized telephone call free of charge. There is no distance limit and it is very convenient. Features: 850/900/1800/1900MHz four-band, can work in the global GSM network.No telephone charges. When the GSM relay switch receives the call from the authorized number, the first "ring tone" is switched on or off.Security. Use caller ID for identification, unknown callers will be ignored.Add or delete users through SMS text commands.There is no need to provide remote controls or keys for different users.Up to 200 authorized telephone numbers can be configured within a specified time.Relay action confirms the return message to the host or authorized call in the number. This function can be edited by the user.The switching time of the relay is programmable.Multiple applications, suitable for doors, pillars, fences, garage doors, shutters and doors or machines.Specifications: Model: RTU5024 GSM Frequency: 850/900/1800/1900MHz Digital Output: NC/Dry Contact, 3A/240VAC DC power supply: 9-15VDC/2A Power consumption: 12V input maximum 50mA/average 25mA SIM Card: Standard SIM Card Antenna: 50 SMA Antenna Interface Temperature range: - 20 ~ + 60 degree C Humidity range: 90% relative humidity Size: approx. 8.2*7.6*2.7cm/3.2*3.0*1.1in Packing weight: 258g/9.1oz Package list: 1 * GSM Door Opener 1 * User Manual