Add or remove users by SMS Text com mand. The relay close or open time is programmable. Can be operated from anywhere, no distance limit. Quad-band, can work in the worldwide GSM Networks. No need to provide a remote control or keys for different users. Secure - Using caller-ID for identification, unknown callers are ignored. Up to 200 authorized phone numbers can be configured at the specified time. One output with relay rating 3A/240VAC for connecting the switch of the door or machines. Multiple applications. (gates, bollards, barriers, garage doors, shutters and access doors or machines). The relay action will return a SMS confirmation to the owner or authorized call in number, this function is editable by user. No call charges. the GSM GPRS Relay Switch rejects the call from authorized number then carries out the turn ON/OFF action on the first 'ring'. GSM Frequency: Quad-Band 850/900/1800/1900MHz Gigital Output: NC/NO dry contact, 3A/240VAC DC Power Supply: 9-24VDC/2A Power Consumption: 12V Input Max.50mA/Average 25mA SIM Card: Support 3V SIM Card Antenna: 50 ohm SMA Antenna Interface Material: ABS Color as shown Package Contents: 1 x GSM Door Opener 1 x antenna Only the above package content, other products are not included. Note: Light reflection and different displays may cause the color of the item in the picture a little different from the real thing. The measurement allowed error is +/- 1-3cm.