KKmoon GSM Door Gate Opener Remote On/Off Switch Free Call SMS Command Support 850/900/1800/1900MHz Quad 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. Up to 200 authorized phone numbers can be configured at the specified time. Multiple applications. (Gates, bollards, barriers, garage doors, shutters and access doors or machines).