The +5V supply line (VCC) of the module is linked to the 5V line of the Arduino. GND of the module is the common (0V) connection. The digital signal output to be detected (usually marked ... Arduino ...

Block Diagram. The security system comprises of an Arduino Uno microcontroller and a standard SIM900A based GSM/GPRS modem. The whole system can be powered from any 12VDC/2A power supply unit/battery.