In this project we are going to learn how  to control a relay connected to a PIC microcontroller with an SMS using mikroC compiler. This relay could be used in many applications to Switch ON or OFF devices such as an electric bulb, or opening a security boom gate like in this example. A security access control can be implemented at apartments or housing complexes, when a visitor arrives at the gate, he/she can phone the visited person who can send an SMS: "OPEN" to the gate cellphone number, upon receiving this message from the GSM module, the PIC will trigger the relay to open the gate and then close automatically the gate after a short delay or after the car has entered the into the housing complex (Infrared beam detectors could be used to detect if a car has passed the gate).