features remote on/off switch by authorized phone free calls, which can be operated from anywhere, no distance limit, very convenient. Features: *850/900/1800/1900/2100MHz bands, can work in the worldwide GSM networks. *No call charges. The GSM Relay Switch answers the call from authorized number then carries out the turn ON/OFF action on the first \'ring\'. *Secure - Using caller-ID for identification, unknown callers are ignored. *Add or remove users by SMS Text command. *No need to provide a remote control or keys for different users. *Up to 200 authorized phone numbers can be configured at the specified time. *The relay action will return a SMS confirmation to the owner or authorized call in number, this function is editable by user. *The relay close or open time is programmable. *Multiple applications. (Gates, bollards, barriers, garage doors, shutters and access doors or machines).