... underground, Oil well far away, Tunnel ventilation, Rural power station etc.Smart GSM Socket protects you from dangerous, inconvenience, and saves ... SMS (Phone Message)The Owner No can control the GSM Switch to through Call (Without any cost)4 digital ... sure it safely controlledStatus Remember after power off.Reset function if the password forgotten.Specification:1. GSM frequency 900/1800 Mhz ( ...