Applications include the remote control of heating in holiday homes, lighting, engine pre-heaters, aviation engine heaters, irrigation systems, water well pumps, pumping stations, cabin heaters, resetting of remote servers, arming and disarming security systems, access control of gates and garage doors.
I personally use two of these devices. I've soldered contacts onto the remote key fob for my remote car starter and have attached these wires to the switch on the GSM device. When I call the GSM devices SIM card, the switch is activated and it connects the two contacts on the key fob to start my vehicle. This triggers my remote car starter and starts the car, all from a quick call from my cell phone. The device can be conveniently mounted under the dash!