He’s using an Arduino Uno and an Ethernet breakout board to hook it up to the network. This allows him to send text messages to himself when the alarm system is armed, disarmed, or triggered.

Making your own security system isn't too hard, but if you'd like a super cheap and simple method, Instructables user deba168 shows how to make a wireless motion detector with an Arduino.

The device also keeps track of temperature and humidity. The entire system can be controlled via a web interface. The Arduino serves a web page that allows the user full control over the alarm.

However, if you’re just looking to catch a sandwich thief at work or a cat spilling over all you water bottles, then Make shows you how to build an alarm system with an Arduino and a USB camera.