This project represents a simple SMS alarm system made with Arduino that allows you to arm or disarm via SMS message. Also when the alarm is triggered you’ll get a SMS notifying you that. And because I know that is very hard to type messages the included android app will help your fingers to rest 
Needed components
- Arduino Uno
- A-GSM shield (a-gsm shield distributors or order online)
- Bread board or prefboard
- laser diode
- photoresitor(LDR)
- 10k resistor
- leds
- wires for connections
How it works
The laser diode and photoresistor creates a light barrier sensor. When armed and the light barrier is breached the SMS alarm system will send an SMS alert to the predefined alert numbers. The system have 3 states, which are not armed, armed and alarm triggered. The state of the alarm you can see on the 6 led’s that are connected to the arduino uno board. Arduino program is so designed that you are able to arm or disarm the system only from allowed phone numbers. If you are really paranoiac you could modify the software for the SMS alarm system so that it’s sending encrypted SMS. For this you have to change the AppInventor software and arduino code a little bit.
For communicating with A-GSM shield I used their latest example code called “kickstart for Arduino”. This is like a library for the A-GSM shield and will help you a lot to achieve your goal with your project. In my case I strip/and modify a little bit the code to suit project needs.
Software
I put the Arduino part of the code on GitHub due to the A-GSM library. You cand download from the below link:
https://github.com/roroid/SMSAlarm
Connections:
AppInventor
For the android app you need a button for arming/disarming the system and a log label for receiving system messages. Below you can see my design and my app:
You can download AppInventor source code and apk from here:
SMSAlarm in the wild