This is a GSM alarm system based on the Arduino Nano and SIM800L boards. This project is designed for maximum autonomous working time e.g. powered by the 18650 battery. When the system is in IDLE mode, it 'sleeps' and wakes up when the interrupt on pin 3 is triggered. If you want to get maximum performance, de-solder the led's from the arduino board and disable the voltage regulator.

1. Solder all components together (note that the SIM800L board works between 3.7V and 4.2V, and the interrupt pins on the Arduino Nano are 2, 3).
2. Edit the values in the #define statements at the top of the sketch (phone number, interrupt pins, timeouts).
3. Put the libraries from the libraries project directpry in the C:\Program Files (x86)\Arduino\libraries directory.
4. Compile, upload and enjoy.